Reinvestigation of the vacuum ultraviolet spectrum of CO and isotopic species: The B1Σ+ ↔ X1Σ+ transition

JOURNAL OF MOLECULAR SPECfROSCOPY

121,309-336 (1987)

Reinvestigation of the Vacuum Ultraviolet Spectrum of CO and isotopic Species: The f3’2+ t+ X12+ Transition M. EIDELSBERG,* J.-Y. RONCIN,? A. LE FLoCH,$ F. LAUNAY,* C. LETZELTER,* AND J. ROSTAS§ +Observatoirede Paris, Section de Meudon, D&atiement &AstrophysiqueFondamentale et VA 812 du CNRS, 92195 Meudon Principal Cidex, France: tEquipe de Spectroscopic(VA 171 du CNRS), Ecole des Mines, 158 Cows Fauriel, 42023 Saint-Et&me Cidex, France; $Dipartement de Physique, UniversitCde Tours, 37200 Tours, France; and &&oratoire de PhotophysiqueMolkulaire (CNRf+B&. 213. UniversitCde Paris&d, 91405 Orsay Cidex, France

The vacuum ultraviolet band spectrum system B’Z+-X’Z+ of ‘2C’60, ‘3C’b, ‘%?‘O, and r3Cr80has been extensively invest&ted both in absorption and in emission with the Meudon Observatory national 10-m vacuum qzectro8raph.A band lying at 109.9nm in ‘%‘60 is observed for all isotopesbut only in absorption. It is shown to be the B-X(2-0) band. Molecular parameters of the B(u = 0,1,2) levels have been derived from simultaneous least-4uares fits of the absorption and emission data pertaining to each of these vibrational levels. In addition, a simultan~us fit of the data for the different isotopes provided mass independent Dunham coefficientsand equilibrium constants for the B state.Our values obtained for w, and w,x, contbm the recent determinations which are in disagreementwith the valuestabulated in standard references.The emission bands exhibit sudden weaken@ typical of predkciation. This pmdkociation further manifests itself in the u = 2 level by a conspicuous broadening of the absorption lines. It may also be the cause of the displacement and anomalous B values observed for this level. From the Dunham coefficients,the following molecular constants (in cm-’ except for rJ for the B statehave been derived r.= 1.1197 A. T, = 86926.9

’WO ‘3~160

‘PO 13Cr80 ‘dCc160 8

We

W&e

2161.7~ 21 13.56 2109.5r 2060.12 2071.52

39.8, 38.08 37.93 36.18 36.58

B. 1.9613’ 1.8749 1.867, 1.7812 1.8010

me

1060,

0.0262 0.0245 0.0244 0.022, 0.0231

6.5 6 5:: 5.4 5.5

1987AcademicPress,Inc.

1. INTRODUCTlON Carbon monoxide is the most widely observed interstellar molecule and therefore plays an important role in the study of the interstellar medium. The various isotopic species of CO are often used as tracers to determine the hydrogen content of molecular clouds and to map the distribution of matter. The abundance of CO in interstellar clouds is dependent on the dissociation processes induced by the UV radiation field. It was suggested by Bally and Langer (I) that the photodestruction rate of CO through predkxiation of discrete states could be largerthan that due to continuum absorption. 309

0022-2852/87 $3.00 0 1987by AardemicPleas,Inc. Au rightsof reproduction in any form r*lcrved. c&yli&l

310

EIDELSBERG ET AL.

This effect would provide an explanation of the anomalous isotope ratios often observed in molecular clouds through self-shielding effects which could affect differently the various isotopes of CO. Rredissociation in discrete absorption lines is also affected by coincidence with other molecular lines, principally Hz (2). Such processes are now systematically included in models of molecular clouds (3, 4). These studies require a better knowledge of the parameters of the states of CO so that accurate absorption wavelengths for the various isotopes can be determined. New high-resolution laboratory data concerning the absorption cross section and photodissociation probability are also needed. The present work, which concerns the spectroscopy of the B’Z+ state of CO, is part of a more general effort to obtain better and more complete data on this molecule in the energy range (20- 13 eV) where the interaction with UV radiation might influence the photochemistry of interstellar molecular clouds. The CO molecule has been the subject of extensive spectroscopic investigations, the results of which have been reviewed (5-7). Recently, high-resolution spectra of the A-X system have been analyzed in detail (8) and new techniques of laser induced fluorescence have allowed the characterization of a new state of CO: D’ ‘Z+ (9). The only high-resolution spectra of the B-X system were obtained in absorption by Tilford and Vanderslice (10). They analyzed the (O-O) and (1-O) bands in ‘2C’60 and 13C160. The last published work in emission was done at low resolution 50 years ago, by Read (11) who identified the bands involving the o’ = 0 and u” = 0, I,2 states. Until now, most of the available information about the B’Z+ state has been deduced from the study of the Angstrom band system B ‘IF --, A’II in ‘*CL60 (I2-25), 13C160, ‘*Cl80 (16, 17), and ‘3C’80 (18-20). However, the numerous perturbations of the A state (8) complicate the analysis and limit the accuracy of the B-state parameters derived from it. For ‘*C160, Le Floch and Amiot (13) have recently obtained reliable term values for the B state horn an analysis of a Fourier transform spectrum of the B + A transition combined with the accurate set of A-state term values determined by Lc Floch et al. (8). Other transitions involving the B state (C’Z+ + B’Z+, E’II + B’Z+) have also been observed in Fourier transform spectroscopy (21) for ‘2C160 and 14C160.Predissociation of the B state had been observed in the B +,4 system as a sudden weakening in the emission bands (22-24) and in VUV one-photon laser spectroscopy (25) and by optical-optical double resonance techniques (26, 27). In the present work, photographic emission and absorption spectra of the B-X transition have been obtained at high resolution with the Meudon Observatory national 10-m vacuum ultraviolet spectrograph. Four isotopic species of CO were studied: ‘*Cl60 13C160, ‘*C180, and 13C180.The systematic study of the isotopic spectra and the deiermination of isotopically invariant Dunham coefficients provide improved molecular parameters for the B state. The predissociation earlier observed for the u = 0 and u = 1 levels in the B + A transition has been observed for the first time in the B + X transition, and a second weakening of the ( l- 1) band lines at higher J has been discovered. The extensive isotopic studies allowed unambiguous assignment of the (2-O) band. This band which does not appear in emission is conspicuously broadened in the 12C160 absorption spectrum. It is argued that the B state is probably predissociated by the repulsive part of the D ’ ‘Z+ state which has been recently observed (9). This interaction would also be responsible for the shift observed in the u = 2 level of the B state.

VACUUM ULTRA-VIOLET II. EXPERIMENTAL

SPECTRUM OF CO

311

DETAILS

The spectra were recorded on Kodak SWR plates by means of the Meudon Observatory 10-m Eagle mounting VUV spectrograph. This instrument is fitted with a concave Jobin-Yvon holographic grating (R = 10.685 m, 3600 lines/mm) which gives a plate factor of about 0.025 nm/mm in the tirst order. The resolution limit is 8 X low4 nm (i.e., 0.60 cm-’ at 115 nm) with a 30-pm slit width. The emission spectra were obtained using a discharge lamp’ which, with a magnetic field of about 0.1 T, can be operated at a pressure as low as a few lo-* Torr. This pressure is lower by two orders of magnitude than in ordinary discharge lamps, thus reducing self-absorption at short wavelengths as previously reported in the case of Hz and N2 (28, 29). The lamp was operated at 400 V, 400 mA. Exposure times varied from 5 min to 5 hr. The continuum background used for absorption spectra was emitted by a BRVtype plasma source (30). This is a windowless source, operated at a pressure lower than 1Oe5Torr, which emits light pulses of about 1 ~sec duration with a 1-Hz repetition rate. The light was focused onto the spectrograph entrance slit by means of a goldcoated toroidal mirror. Carbon monoxide gas was introduced into the spectrograph body, which thus acted as an absorption cell of about 20 m path length. The pressure inside the spectrograph was varied from 5 X 10e5 to 5 X 10-l Torr and the exposure times from 1 to 2.5 hr. Three types of gases were used to carry out the investigations: (i) 99% purity natural CO from Air Liquide, (ii) 99% isotopic purity 13C”j0, and (iii) 97.6% isotopic purity ‘*C’*O. The isotopic gases were provided by Commissariat a l’Energie Atomique. Reference lines from Cu II, Ge II, Cl I, 0 I, N I (31) were obtained by flowing helium in a water-cooled windowless hollow cathode discharge lamp operated at 500 V, 400 mA, and were recorded in the same grating order. The plates were measured by means of the Meudon Observatory photoelectric comparator (32) which provides an accuracy of 1 pm for the position of the unblended lines. The shifts which may be observed between the reference and measured spectral lines, due to a possible different illumination of the grating by the two sources, was determined by reference to two Ar I impurity lines appearing in the background continuum. The corrected wavenumbers were veritkd to be consistent with the very precise values derived from the previous observations of both (B --* A) (13) and (A-X) (8) spectra. The uncertainty on the absolute wavenumbers is estimated to be kO.1 cm-‘. III. DESCRIPTION

OF THE SPECTRA

The most extensive study concerns the ‘*CL60 and 13CL60species, which have been observed both in absorption and in emission. ‘*C”O has been recorded only in absorption: the ‘3C’80 bands have been observed on the 13C160spectra due to an unexpected abundance of 13CL80in the gas sample. Twenty-two bands were rotationally analyzed, eighteen for the first time, as indicated in Table I. In absorption, the (O-O)and (1-O) bands which had been previously observed and analyzed for ‘*Cl60 and partially for 13C160 have also been analyzed for the less ’ This was suppliedby Instruments S.A., France, and registered with the Agence Nationale pour la Valorisation de la Recherche under Contract No. 7 296 800.

312

EIDELSBERG ET AL. TABLE I Band Center Wavelengths (in nm) of the B’Z+-X’Z+ Bands Analyzed in This Work v-

1

0

2

3

V'

‘2c’60

115.05

a.b

117.96

*

120.96

8

13cl6(-J

115.05

a.b

_117.90

a

_120.65

a

12clq-J

115.05"

13ci6(-)

115.05

a.b

_116.01

a

121.00

a

117.94

a

120.66

a

‘2c’60

0

112.36

a.b

115.13

13~160

112.42

a.b

115.13

12~160

112.42"

13c160

112.48

'2~160 13~160

1

2

a

a.b

109.90" 110.00"

12cl60

,t"

13c160

110.11

Note. Underlining indicates a band analyzed for the 6rst time in this work. ’ Emission. b Absorption.

abundant isotopic species ‘*C’*O and 13C’80. The assignment of the band at 109.9 nm has been the subject of controversy. This band was first assigned to the B + X (2-O) band by Tanaka et al. (33). Later, Tilford and Vanderslice (10) reassigned it to the (O-O) band of a new transition j3Z+ + X1X+. Their assignment was supported by the observation of another band at 107.3 nm which could reasonably be attributed to the (1-O) band of the same transition. Another argument presented in favor of this assignment was the relatively strong intensity of the 109.9~nm band with respect to the B-X (O-O) and (1-O) bands. However, none of the corresponding bands were observed, at that time, in ‘3C160. The present absorption spectra show marked differences from those obtained by Tilford and Vanderslice, since we do observe bands, respectively, at 110.00, 110.01, and 110.11 nm for ‘3C160, ‘*C’*O, and ‘3C’80 corresponding to the band at 109.9 nm in r2CL60. On the other hand, no absorption whatsoever is observed around 107.3 nm in any of the isotopes. The wavelengths measured for the four isotopes are perfectly consistent with their assignments to the (2-O) band. Comparison of estimated* and observed isotopic shifts given in Table II shows that the 109.9~nm band observed on our plate cannot be a (O-O) band but is z Considering the inconsistencies in the various values for oc and o& of the B state given in the literature (see sect. V), we have calculated a first estimate for the isotopic shifts from the usual isotopic relations using the oc and o& values of the CO+ ground state. This choice is justitied by the electronic character of the B state, which is the lirst member of a Rydberg series converging to the CO+ (X’Z’) ground state.

313

VACUUM ULTRA-VIOLET SPECI’RUM OF CO TABLE II Observed and Calculated Vibrational Isotopic Shifts (in cm-‘) for the (B-X) Bands ‘4 Bands

& = “(%‘@30) - “<‘CIO)

‘cl0

Calculated

Observed

a

o-o

1-o

c

13cl60

0.97771

0.6

-

0.4

-

0.8

12c180

0.97584

0.7

-

0.4

-

0.2

13ClttO

0.95299

1.3

-

0.9

-

1.2

13C160

50.0

44.4

12c130

54. 1

48.1

48.1

93. 7

93.5

13c180

2-o

b

13C180

105.4

99. 3

12c130

107.6

13c130

209. 1

44.2

85.8

32. 0

93.0

33.9

181.2

173.3

’ Calculated with w., u& of CO+(X’Z+) (Table VI). b Calculated with w,, W;S,of CO@%+) obtained in the present work (Table VI). c Difference of the band origin wavenumbers.

indeed the B-X (2-O) band. The consistency of the observed intensity with the FranckCondon factors further supports this assignment. In emission, bands originating horn B, 8 = 0 and 1, and involving X, v = 0, 1, and 2, have been observed (Table I). Bands of the same sequence overlap heavily and the rotational structure is somewhat congested in some cases where several isotopic species are observed simultaneously. AU the emission bands show the sudden weakening expected from previous work (22-25, 27) for example, in ‘*C?O, above J’ = 37 for u’=OandJ’= 17forv’= l.Theu’= 1caseisilIustratedinFig. l.Forthestrongest bands, namely (O-O) and (l-l), lines are observed after the intensity discontinuity, up to J - 60 and 40, respectively. These exposures reveal a second intensity weakening in the Pbranch of the (l-l) band of ‘*Cl60 (Fig. 1) and of 13CL60which had not been previously observed. Such weaken@ of the emission lines are characteristic of upper state predissociation. Further manifestations of the B-state pred&ociation are the absence of emission originating from the 21= 2 level and the broadening of some (2-O) absorption lines (Fig. 2). The v = 2 levels of the B state are not only broadened but also perturbed as can be seen in Fig. 2A, where the P( 13) and R( 11) lines of the 12C’60 (2-O) band are obviously displaced. IV. ROTATIONAL ANALYSIS AND DETERMINATION OF THE MOLECULAR CONSTANTS

The spectrum of the B-X transition consists of strong R and P branches separated by the origin gap (-4B). For most bands, the lines have been easily numbered in J.

314

EIDTSISBERG ET AL. 112.2

112.4

112.3

I

112.5

I

I

nm

I

B-X

R

30

25 I

114.9

20

15

10

5

I

115.0

01

5

10 I

115.1

20

30

P I

115.2

I

115.3 nm

FIG. 1. Predissociation of the CO B’Z+, u = 1 level as observed for ‘2C’60. (a) B + X (1-O) band in absorption; (b) B + X(1-0) band in emission; (c) B + X ( 1- I) and (O-O)bands in emission. A first intensity weakening starting at R( 17) and P(19)appears clearly in the (1-O) and ( 1- 1) emission bands. A second weakening occurs at P(37) in the ( l- 1) band. Note the intensity oscillations appearing after the disuWintity. The heavily exposed feature at J = 17- 18 in the (I- 1) band is an impurity (0 I) eo@sioc line.

In addition, the J assignments have been checked by comparing the combination differences R(J - 1) - P(J + 1) = A#“(J) with the appropriate A#“(J) = F”(J + 1) - F”(J - 1) of the ground state. This provides unambiguous assignments even in the heavily overlapped emission bands, namely the (O-O) and ( 1- 1), (0- 1) and ( l-2), and (O-2) and (l-3) bands. Assignments and wavenumbers of the rotational lines of all the observed bands for the four isotopic species are given in Table A.1 of the Appendix. The molecular constants have been determined from the measurements by a leastsquares fitting procedure in which the measured wavenumber of each line is compared to the corresponding difference of the calculated upper and lower term values. Since the CO (X’Z+) ground state has been extensively studied by microwave and infrared techniques, its rovibronic term values are known for all isotopic species with an uncertainty smaller than low5 cm -I. Therefore in all the data fits described below, the molecular constants of the ground state have been held fixed at the very accurate values recently derived by Guelachvili et al. (34) from infrared Fourier transform spectroscopy of seven isotopic species. The ground state term values were expressed as a Dunham-Watson power series (35,36) involving the 35 mass-independent coefficients tabulated by Guelachvili et al.: Ei(V,J) = z pTck’*+‘)Ud1 + rndA&M=+ A$QMo)] D+ i k[J(J+ l)]’ (1) ( 1 k.1 where i refers to a given isotopic species, pi is its reduced mass, the VWare the reduced Dunham coefficients, and Au the mass-independent mass-scaling factors.

VACUUM ULTRA-VIOLET

I

I

109.9

I

I

110.0

SPECTRUM OF CO

I

I

I

I

110.1 nm

110.2

FIG. 2. Absorption spectrum of the B-X (2-O) transition. Absorption path, 20 m. (A-C) Natural CO, nqe-ctive pressures:2 X IOe2, 7 X lo-*, 5 X 10-l Tom. (D) Enriched ‘3C’60, pressure: lo-* Torr. (E) Enriched ‘?*O, pressure lo-’ Torr. The isotopic displacement is obvious and leaves no doubt about the assignment of this band. ‘%160 has been observed both as an impurity in ‘2c’60 (C) and in isotopically enriched ‘%?O (D). 13C’80 has been observed only as an impurity in 13C160(D). The predkxktion broadening is very apparent in the ‘%?O spectm, especially for higher J lines in the P branch and throqgh ditTusenes in the R branch. other isotopes exhibit less pronounced broadening. Note the local perturbation at R(12) and fll4) in the ‘%‘60 spectra.

In a first step, the term values of the B state were represented for each isotope i by the usual expression:

316

EIDELSBERG ET AL.

where G”(0) is the zero-point energy and T is the term value referred to the 11 = 0 level of the appropriate isotopic species ground state. The parameters T, B, and D of each vibrational level of the B state have been determined by a direct, weighted, leastsquares fit of all emission and absorption lines involving the vibrational level considered. The weight associated with each line was taken as the reciprocal of the square of the experimental uncertainty. The number of observed levels and observed lines varies considerably with the vibrational level and the isotopic species. In particular the data set pertaining to the o = 2 level is quite restricted since no emission spectrum could be obtained and no lines above J = 13 have been included, because they are either too weak or obviously perturbed. Results of this level by level fit procedure are displayed in Table III. From this table, it can be immediately seen that the BZ value is anomalous with respect to the B. and B1 values. Indeed the fact that BO - B1 N 2(BI - Bz) for all isotopes reveals the occurrence of a severe perturbation of the B, u = 2 rotational levels, which precludes their use for the determination of a Morse potential curve. However, the availability of data pertaining to 2, = 0 and u = 1 for four isotopic species provides an overdetermined set of equations from which the parameters of the Morse curve can be extracted. This result is best achieved by a determination of the massindependent Dunham coefficients which can be obtained by a comprehensive fit of all lines (893) pertaining to both the u = 0 and u = 1 levels of all the available isotopic species. The quantities E(u, J) were calculated for the B state, u = 0 and u = 1 levels, with the expansion already used for the X state. The term values are thus defined as T(u, J) = T, + E(u, J) where T, is the electronic energy of the state including a possible electronic isotopic shift. In a tirst step the parameter T, was left free to adjust independently for each isotope. The result showed that the T, values obtained did not differ significantly, indicating an isotopic electronic shift smaller than our experimental accuracy (0.1 cm-‘). Consequently, a new fit of the same data was carried out with a single parameter T,. Seven significant molecular parameters, namely T, and six Dunham coefficients, have been obtained. They are given in Table IV together with the corresponding ground state parameters. As stated above, the u = 2 rovibronic levels cannot be rep resented by Eq. (1). Their displacement relative to the position extrapolated using the Dunham coefficients of Table IV depends linearly upon J(J + 1) and can be represented by Avi(U = 2, J) = AGz,i+ &iJ(J+ 1) where AG,,i represents the vibrational shift, and ABz,i the rotational constant defect for the ith isotopic species. These parameters were determined by an overall leastsquares fit of the lines involving the Ui = 2 levels using the expression Ei(U=2,J)=T~+AG2,i+~;“*U

lO(

U+’

2)

+/.L”U ’ -(

+J(J+ l)[~~1~~~+~~,~+~~3’z~~~~+~)]+Jz(J+

U+’

2)

~)‘[~r’~o2+r;‘“U,,(u+f)l

VACUUM ULTRA-VIOLET

317

SPECTRUM OF CO

TABLE III Molecular Constants (in cm-‘) for the B’Z+ State of CO Isotopic Specks 12C16~

1 e 1060

13~16~

T 0 106111

12~160

7 B 1060

1.921902(201

1.6779(171

6.764(21)

7.361151

7.7

13~160

1 I3 1060

V' =

V' = 0

66916.79(5)

V' = 2

1

90906.45(6)

66954.14(21

1.66256l143

1.63610~20)

1. 796Om

6.176~48)

6.69~13)

7.0

0.114

0.141

V' =

V' = 0

66916.42(4)

8

1952.01

2037.35

0.095

V' = 2

1

90699.15(41

66950.24(6)

1.65553(23)

1.63100(42)

1.7691W

6.257~~

6.35~54)

6.9

0.074

0.049

V' =

v' = 0

66917.34(a)

'

1946.94

2033.62

0.047

"' = 2

1

90614.60(11)

66904.61,s)

1. 76960(42)

1. 74733(33)

1.7060(11)

5.6

6.0

6.3

'

'

1997.47

AG 0'

0.172

0.113

0.104

8

1969.60

2062.14

AG o't

90966. 13w

1.946166(72)

AG ;"

V' = 2

1

66998.32(4)

66916.16l31

AG oz

V' =

V' = 0

0.179

'

1909.53 0.174

0.037

Note. tZ is the unitless viuiamx. The uncertainties in parentheses are 3 (r from the least-squares fit expressed in units of the last quoted digit of the coe5cients. ’ Value of D calculated from the Dunham coefficients of Table IV and held constant in the least-squares fit.

where T, and the Vu parameters have been held fucedto the values obtained from the t, = 0 and 1 level fits and given in Table IV. The scarcity and relatively large uncertainty of the experimental u = 2 data set-due to broad, blended, or perturbed linesprecluded a determination of A& for each isotopic species, and only an “average” A& value could be determined. The values derived for AGz,i and AB2 are given in Table V. The observed and calculated displacements of the u = 2 levels relative to the positions extrapolated using the Dunham coefficients given in Table IV are plotted against J(J + 1) in Fig. 3. It must be emphasized that the observed displacements,

318

EIDELSBERG ET AL. TABLE IV Dunham Coefficients for the B’Z+ and X’Z+ States of CO’ b

B&C+

c

x'c+

66928.92(201

0.0 5661.366W

5660.4(14) -273.

4

1~791

-91.106(l)

13.44736m3)

13.243466(91

-0.4719(971

-0.ai4263~43

-3.067(10)x10-•

-2.6772(5)x10-'

-6.45(46)x10-'

1.116~x10-~

'Valid only for II < 1 (see the text). The equilibrium constants and reduced masses are those of the relevant isotopic species. The Vu are expressed in cm-’ amuU2+’(amu = atomic mass unit), T, in cm-‘. b Expression in terms of the equilibrium molecular parameters. ’ Present work. d From Ref. (34). These parameters belong to a set of 35 coefficients which are required to calculate the ground state term values.

although increasing with decreasing isotopic mass, are not isotopic shifts in the usual sense, i.e., they do not follow the usual mass scaling law. They are related to the predissociation of the B state, and it may be observed that the shift and broadening of the rovibronic levels increase with decreasing mass, i.e., with increasing energy of the level. The experimental term values derived by proper weighted averaging of the measured line frequencies are given in Table A.11 of the Appendix.

TABLE V Observed Vibrational and Rotational Shifts (in cm-‘) for the B’Z+, u = 2 Level

*2

-0.0174s)

. . .

Note. The dispersion of the data does not allow the determination of separate A& for each isotopic species.

VACUUM ULTRA-VIOLET o_

loo

SPECTRUM OF CO

200

300

319

J(J+l' 1 .Qc 160 0 "% "0 , I.?/B. I$ B c "0

FIG. 3. Shifts of the rotational term values of the B’Z+ (u = 2) level. The difference between the observed term values and the ones calculated from the Dunham coefficients of Table N is plotted against J(J + 1). The straight lines represent AG = AG, + AB2J(J + 1) (see Table V). The I%‘@0 plot has been shit&d upward by 1 cm-’ for clarity. The perturbation occurring above JB > 12 for ‘W60 can be observed directly in Fig. 2.

V. DISCUSSION

V.1. Equilibrium Constantsand Isotopic ShiJis The equilibrium values of the molecular constants can be derived for each isotopic species from the Dunham coefficients given in Table IV using the general relationships. They have been calculated for the four isotopic species ‘zC160, 13C60, ‘*C1*O, and 13C’80 studied in the present work and for the “C160 species whose (B * A) (37) and (E * B, C + B) (21) transitions have been recently investigated. They are compared in Table VI with the corresponding molecular parameters of the ground states of the neutral and ionic ‘2C’60 species. It should be emphasized again that the molecular constants for the B state have been derived only from the lines involving the 11* 0 and u = 1 levels, as in all previous analyses of the B-A and B-X systems, and with the aid of isotopic data. Table VII presents the available results concerning the 12C’60 molecule. The AGIl values, obtained directly from the spectra, are in excellent agreement (within 0.1 cm-‘), but yield significantly different sets of values for w, and w,J=. The discrepancy between the derived w, and o&~ values arises from the data reduction, due to the large correlation (99%) between T,, wp, and w&=. Since the reduced masses of the isotopic species are quite close, new experimental data on the u = 0 and u = 1 levels of other isotopic species, such as i4CL60, would not greatly improve the accumcy of U, and WA=,although it could help to define more accurately the B-state potential curve around u = 0 and u = 1. The values of w, and WJ~ determined in the present

320

EIDELSBERG ET AL. TABLE VI

Equilibrium Molecular Constants (in cm-‘, except p and r,) for the B’Z+ State of CO Isotopic Species’

.5’&+

12C160

6.85621

13cl6o

7.17241

12~ltl~

7.19937

13,reo

7.54937

14C160 d

7.46648

2082.14

2161.7G

39.84

I.9613

0.0262

G.5

2037.32

2f13.!j6

3&O*

1.8749

0.024G

G.o

2033.~i~

2105.53

37.93

1.3677

0.0244

5.9

1987.3*

2c60.12

3&l*

1.7812

0.0227

5.4

155G.04

2071.52

36.53

1.3010

0.023,

5.5

2169.81

13.288

1.93128

0.0175

6.1

2214.z4

EB.I~~

1.97720

O.OlsSG

G.3

XlE’ 12C160

1081.59 c

x2&+ 12C160+

@topic

co co'

Invariants:

re Cn",

Tc (cm-')

BLr+

1.1197

X'f

1.1289

86926. g 0.0

xy+

1.1151

114110.4

’ The molecular constants for X’Z+ of CO and X*Z+ of CO+, given for comparison, are taken from Ref. (7), given for comparison. b Reduced masses (in amu) from Ref. (43). c Ground state zero-point energy from Ref. (34) (1057.55, 1055.54, 1030.88, and 1036.57 cm-’ for ‘%?O, ‘2c’*O, ‘3C’*0, and ‘%?O, respectively). d Calculated from parameters of Table IV, but not observed in the present work.

study agree to within a few cm-’ with the values obtained from the various (B-A) system analyses, but are probably more accurate since they have been derived from the Dunham coefficients obtained from a simultaneous fit of all isotopic data. It is surprising that Tilford and Vanderslice obtained so widely differing values of o, and w&~ values from the 12C’60 and 13C160 (B c X) band data reduction, and it is unfortunate that their values are the ones retained in Huber and Her&erg’s tables3 (7). The molecular constants of i4Ci60 predicted from the Dunham coefficients are in excellent agreement with experimental results obtained while this work was in progress. Domin et al. (37) report AGi,z = 1998.38 cm-’ and Amiot et al. (21) obtain B (u= 0)= 1.7893 cm-’ to be compared to 1.7885 cm-’ derived from Beand (Yegiven in Table VI. 3 This has caused Prasad et al. (19) to give incorrect values of o, and o,& for ‘3C’s0, AG,n value IScorrect.

although

their

VACUUM ULTRA-VIOLET

321

SPECTRUM OF CO

TABLE VII Comparison of the Values (in cm-‘) Reported for the Vibrational Constants of the ‘%‘60 B’Z+ State a

% we AGl/2'

2112.70 15.22 2082.26

b

c

d

e

2160.7

2153.929

2151.25

2161.75

39.3

35.879

34.52

39.84

2082.10

2082.17

2082.21

2082

08

’ Tilford and Vanderslice (IO). b McCulloh and Glockler (14). ’ Rytel(16, 17). d Domin et al. (37). ’ This work. ‘From AG1/Z= w, - 2w&. Note that all the experimental values of AG1,2agree to within 0.2 cm-‘.

Neglecting the electronic isotopic shifts which were found to be of the same order of magnitude as the experimental uncertainty, the isotopic shifts for the (u-0) B-X bands can be calculated from the following relationship

using the constants w,, w&~, and P given in Table VI. As expected, the observed and calculated isotopic shifts are in excellent agreement for the (O-O) and (1-O) bands and differ notably for the (2-O) bands. The discrepancy arises from the displacements of the u = 2 levels which are shown in Fig. 3. The Morse function potential curve (b) constructed from the Dunham coefficients given in Table IV is shown in Fig. 4. It gives an accurate representation of the lower part (up to u = 1) of the B-state potential energy curve. The relatively large value of the anharmonicity constant results in a curve shallower than those of the CO and CO+ ground state&o&& N 2(w&JX -as can be seen in Fig. 4 where a curve parallel to the X2X+ CO+ ground state is also represented (curve a). As discussed above, the u = 2 levels are shifted downward relative to the level which would be determined from both Morse curves. This fact and the value obtained for Bvc2 (Table III) indicate that the actual adiabatic potential curve c is below and, again, more “open” than the Morse curve b. From the value of Buzz, one can obtain a crude approximation of the position of the outer turning point of the observed u = 2 level. If one assumes that the “unperturbed” curve of the Rydberg state is parallel to the ground state of the ionic species, not only are the u = 2 levels shifted, but also the u = 0 and 1 levels. The shifts for the 2, = 0, 1, and 2 levels are given in Table VIII and plotted as a function of energy in Fig. 5, which clearly shows that the shifts increase considerably with u. As discussed in the next section, these shifts arise at least partly from the interaction

322

EIDELSBERG ET AL.

I.20

r,_,(A)

FIG. 4. Approximate potential energy curves for the B’Z+ state of CO. (a) Morse curve for CO+X*Z+. (b) Morse curve for CO B’Z+ based on the Dunham coefficients of Table IV determined from u = 0 and u = 1 data only. (c) Estimate of the actual potential curve.

of the B state with a repulsive state and arc therefore related to a predissociation of the B state. V.2. Predissociationand DissociationEnergy In the present work, the predissociation of the B state is observed in the B-X bands both in emission and in absorption. The experimental evidence consists of(i) a weak-

TABLE VIII Vibrational Term Value G, and Shift (in cm-‘) for the B’Z+ u = 0, 1, and 2 Levels of ‘%?O

0

1059.4

-93.9

1045.8

-33.1

1043.8

-33.0

1

3151.5

-135.7

3033.1

-131.6

3077.3

-131.3

31m.9

-127.3

2

5141.3

-299.5

5035.1

-286.5

5026.9

-295.4

4916.5

-272.8

1019.5

-32.1

Note The shit3 Av is defined as the difference between the observed @ and the calculated term value of the “unperturbed” (diabatic) potential curve which is taken to be parallel to the CO+ (X’Z’) state. Tbe common origin is the minimum (u = -1) of the Morse curve defined by the Dunham coefficients of Table IV.

VACUUM ULTRA-VIOLET

w

V’

0

323

SPECTRUM OF CO

II I

,o

I

2000

4000

,2 G, /cm-’

RG. 5. Shifts of the vibrational levels of the B’Z+ state of CO (see Table VIII).

ening of the emission lines originating from the u = 0 and 1 levels above a critical rotational number J,; (ii) no observation of emission bands originating from o > 1 levels; (ii) broadening of lines in the absorption bands involving the u = 2 level of ‘2C’60 (Fig. 2). The level shiRs observed in the 2, = 2 level of the B state are very probably evidence of the interaction of the B state with a repulsive state. The emission line weakening had already been observed in the (B 4 A) system first for the v = 0 level of ‘2C’60 by Coster and Brons (22), then for the u = 0 and u = 1 levels by Schmid and Gero (23). Later, Douglas and Moller (24) confirmed this observation and observed a similar effect in the corresponding bands of ‘3C160. Klopotek and Vidal (27) and, more recently. Rottke and Zacharias (25) have observed the intensity weakening in the u = 1 level by VW laser spectroscopy. From the plot of the rovibronic energy of the J, and J,+, levels against J(J f 1), Douglas and Moller (24) were able to draw a “limiting curve of pred&sociation” and, by extrapolation to J = 0, determine the energy of the corresponding dissociation limit. In the present work, intensity weakenings are observed in emission in the B + X (O-O), (I-O), and (l-l) bands of 12C160and r3C160 (Fig. 1) and the (l-l) band of ‘3C*80. These new observations confirm the previous ones made in the Angstrom bands. As can be seen in Fig. 1, the first line after the intensity discontinuity is markedly weaker than the following ones. This intensity variation was also observed by Rottke and Zacharias (25) in the B-X (1-O) band in their recent VUV laser excitation experiment. The term values of the last nonpredissociated level and first predissociated level for each isotopic species are given in Table IX and plotted in Fiiure 6. The new data obtained from the ‘3C’80 0 = 1 level increases the weight of the experimental data in the u = 1 region. However, the lack of data for u 2 2 precludes an accurate determination of the actual shape of the curve, and we assumed, as did Douglas and Moller (24), that it is a straight line. Inclusion of the new 13C180 data improves the accuracy of the

324

EIDELSBERG ET AL. TABLE IX

Term Value (in cm-‘) of the Highest Nonpredissociated and Lowest Predissociated Rovibronic Levels Molecule

”

J

12cltIg

0

37

90723.46

90670.33

1

17

90667.19

90736.19

0

39

90664.91

91012.33

1

19

90709.13

90762.61

1

20

90666.52

90741.67

13~160

1301.3(3

T,(J)

Te(J)

Note. The common origin is the minimum of the ground state potential well (u = - 4).

dissociation energy limit, which is now 90 674 5 15 cm-’ above the X’Z+ ground state potential minimum, i.e., 89 592 cm-’ above the u = 0 level of ‘*C160. Spectroscopic observations (9, 38) have established that the B state predissociates toward the first dissociation limit of CO, namely C(‘P) + 0(3P). The predissociating state is therefore one of the 18 states arising from this limit:

400

0

800

J(J*l)

I

E/Clll-'

1

I

ll2c#o

91000-

0 "c "0 h 'SC"0

/ i

90900-

90600 0

1 IO

20

1 30

J

FIG.6.Limiting curve of dksociation for CO X9+.

L 4t

VACUUM ULTRA-VIOLET SPECTRUM OF CO

C(3P) + 0(3P) + X12+, A’II, D’A, I%,

325

D’ IX+, (2)‘II

a’ 32+, a311, d3A, e3Z-, (2)32’, (2)311 (l)‘Z+, (l)‘II, (l)5A, ( 1)5Z-, (2)52+, (2)511. According to Mulliken (39), the decrease of J, with increasing u implies that the predissociating state crosses the B state on the right-hand side of the potential curve (Mulliken “+” case) and therefore the low-lying states, namely X’Z+, a311, A’II, e3Z-, a’ 3E+, I’Z-, D’A, and d3A, cannot be involved in this process. Preliminary results of ab initio calculations presently being carried out by Kirby and Cooper (40) show that the B state correlates adiabatically with the recently observed D’ ‘Z+ state (9) and the resulting double minimum state (B, 0’) dissociates into the ground state atoms. In the diabatic picture, the strong homogeneous interaction between the discrete levels of the B state and the continuum of the D’ state shifts the B levels downward and gives rise to the observed predissociation. In a somewhat similar case, Atabek and Lefebvre (41) have carried out quantitative calculations of the shifts and widths of the vibrational levels of the B, 0: state of Se2 produced by the interaction with a repulsive state. Such calculations require an a priori representation of the diabatic curve. Since not only the u = 2, but probably also the u = 0 and 1 levels are perturbed, it seems reasonable to take a potential curve analogous to that of the CO+ ground state to describe the “unperturbed” Rydberg state. The v = 0, 1, and 2 level shifts derived in this approximation for the four isotopic species are given in Table VIII and represented as a function of the energy and u in Fig. 5. These shilts are also illustrated in the potential curves in Fig. 4. As mentioned earlier, a second weakening of the P lines of the ( 1- 1) band has been observed above J = 35 and J = 36 for ‘2C’60 and ‘3C160, respectively (Fig. 1). The second intensity discontinuity exhibits oscillations similar to those observed in the first one. Unfortunately the elect cannot be observed in the R branch which is masked by the R branch of the (O-O) band. No weakening has been observed in the (O-O) band other than that discussed above (J > 37). The possibility remains that the second weakening occurs for rotational levels higher than J = 64 which is the highest observed in the R branch of the (O-O) band. The energy at which the weakening is observed (-9 1 500 cm-‘) indicates that the predissociating state correlates with the lirst dissociation limit of CO but possibly to a different fine structure component. The B-state predissociation will be further investigated both experimentally through photoelectxic linewidth measurements and theoretically by numerical calculations using appropriate potential curves and interaction matrix elements. V.3. Perturbations In addition to the overall shift observed in the u = 2 level which we attributed to the interaction of the B state with the continuum of the 13’ state, some local level shifts occur in the u = 2 level of the various isotopic species. These perturbations show up clearly in Fig. 3 where individual rotational level energies deviate from the straight line obtained from the fit of the unshifted set of lines. These shifts are small, but significant with respect to the accuracy of the measurements even though the lines are

326

EDELSBERG ET AL.

broadened. The largest shifts (1.5 cm-‘) are observed for J = 13 and 14 of 12C’60, and produce the gaps which can be seen in Fig. 2. The levels above J = 12 are atIected in all isotopic species (Fig. 3). In the heaviest isotope ‘3C’80, the low-J levels are also perturbed. By contrast, no local perturbation has been observed in the u = 0 and v = 1 levels. In particular, our analysis does not confirm the perturbations observed in the B-A emission spectra by Janjic et al. (42) for the v = 1, J = 7 and 8 levels of i3Ci60. If there is any perturbation, the shifts of the relevant lines must be smaller than 0.1 cm-*, which is the experimental uncertainty in the present work. Actually, weak perturbations (line shift < 0.02 cm-‘) have been recently detected in the (O-O) band of the Fourier transform spectra of the (C + B) and (E + B) transitions of 12C’60 and i4Po (21). VI. CONCLUSIONS

Results of an extensive investigation of the absorption and emission spectra of the B-X transition in four isotopic species of CO have been reported. Simultaneous analysis of the data for four isotopic species has allowed the determination of mass-independent Dunham coe5cients which yield a consistent set of molecular parameters for u < 2. From this representation of the B state, which is valid up to 3 150 cm-’ (u d 1) above equilibrium, term values for the t, = ‘0 and 1 levels can be calculated for any isotopic species. They are given for 14C“j0 in Table A.111as an aid for the analysis of spectra involving the B state. The emission spectra, obtained at very low pressure, display intensity weakenings which had not been observed by conventional spectroscopy in the VUV, thus confirming the predissociation of the B state and the value of the ground state dissociation energy. They also provide data on high rotational levels which were not previously available. A second intensity weakening occurring at higher J values could thus be observed for the first time. Characteristic intensity oscillations have been observed around both discontinuities. The u = 2 level which can be observed only in absorption has been assigned unambiguously. The lines of the (2-O) band are conspicuously broadened in the i2Ci60 isotope, and the 11= 2 level is shifted downward in all isotopic species. These observations are interpreted as other effects of the predissociation of the B state. It is argued that this predissociation is due to the repulsive part of the shallow D’ ‘Z+ state. A theoretical analysis of the interaction between the B and D’ states has been undertaken. The detailed experimental results now available should allow an accurate determination of the diabatic potentials of both states and of their interaction. APPENDIX

The rotational line wavenumbers and their assignments are given in Table A.I. The experimental term values are given in Table A.11. The term values calculated for 14C160are given in Table A.111.

327

VACUUM ULTRA-VIOLET !PECTKUM OF CO TABLE A.1 Vacuum Wavenumbers and Line Assignments for the B’Z+-X’Z+ Transition of CO: (a) ‘ZC’b, (b) ‘3C’b, (c) ‘%?80, (d) %‘*O

a J

R(J)

0 :

90992.01 90995.64 90999.12 91002.67 91006.00 91009.25 91012.48 91015.43 91018.51 91021.47 91024.35 91027.27 91027.27 91034.26 91034.26

3 4 ii 7

a

9 10 11 12 13 14 15 16 17 18 19

o-o

2-o o_c

0.12 0.09 -0.01 0.05 -0.01 -0.07 -0.05 -0.22 -0.18 -0.16 -0.13 0.04 -2.62 1.80 -0.67

ii ::

P(J)

0-c

J 0

90904.30 90980.36 90976.36 90972.20 90960.ti 90963.68 90959.30 90954.78 90950.31 90945.68 90941.06 90936.12 90930.89 90925.17 90922.07 90916.75 90912.17 90906.21 909oo.79 90895.04 90889.32 90882.80

0.01 0.01 0.03 -0.01 -0.01 -0.04 -0.05 -0.10 -0.01 0.00 0.11 0.00 -0.31 -1.03 0.97 0.83 1.53 0.94 0.98 0.79 0.72 -P.O6

1-o

:

15 16 17 18 :i :: 23 24

:i J

7

a 1: 11 12

:: :i

I/ 18 19 20 21 22 23 24 15 26 27 28

R(J) 89ow.ll3 8Yoo5.87 89009.71 89013.56 89017.41 89021.28 89025.10 89028.92 89032.69 89036.60 89040.46 89044.13 89048.02 89051.85 84055.61 89059.40 89063.18 89066.93 89U70.75 89074.44 89076.23 89081.91 89085.69 89089.44 89093.09 89096.76 89100.51 89104.17 89107.36

O_t -0.14 -0.14 -0.16 -0.13 -0.11

-0.08

-0.09 -0.10 --0.16 -0.07 -0.02 -0.16 -0.08 -0.05 -0.08 -0.08 -0.08 -0.10 -0.04 -0.10 -0.06 -0.11 -0.04 0.00 -0.04 -0.07 0.04 0.05 -0.38

f’(J) a0994.39 88990.61 88986.79 88992.99 88979.11 88975.36 88971.53 88967.56 88963.68 88959.76 88955.86 88952.07 88948.15 88944.34 88940.40 88936.50 00932.60 RR9X. 75 88924.96 88921.10 88917.47 88913.45 88909 63 68905.77 88901.98 88898.39 88894.40

o_c -0.08 -0.02 0.01 0.05 0.02 0.12 0.15 0.03 0.00 -0.07 -0.11 -0.05 -0.11 -0.07 -0.15 -0.17 -0.21 -0.19 -0.12 -0.10 0.15 0.02 O.O8 0.12 0.22 0.54 0.47

27 :: 30

::

33 34 35 36 37 :i 40 41 42 :: 45 :; 48 :: :: 53 54 :,” :i 59

62 62 63

l

Blended.

R(J)

o-c

86920.22 86924.11 86928.04 86932.05 L16936.07 86940.36 86944.53 86948.80 86953.11 06957.47 86961.84 86966.32 86970.81 06975.32 86979.88 86984.52 86989.23 86993.94 86998.73 87003.53 87008.42 87U13.36 87018.31 87023.30 87028.32 87033.41 87038.53 87043.72 87048.93 87054.14 87059.45 8J064.82 87070.21 87075.60 n7081.01 87086.52 87091.93 87097.39 87102.93 W108.55 87114.24 w119.93 87125.62 87131.32 W137.16 87142.93 87148.70

0.14 COY 0.02 -0.03 -0.10 0.04 0.01 0.03 0.04 0.05 0.02 0.06 0.05 0.01 -0.01 -0.01 0.02 -0.01 0.01 -0.01 0.01 0.04 0.03 0.02 0.00 0.00 0.00 0.03 0.02 -0.01 0.01 0.06 0.07 0.06 0.04 0.07 -0.02 -0.11 -0.15 -0.14 -0.09 -O.“J -0.08 -0.12 -0.04 -0.06 -O.Oi

Wm.;; 87166:37 87172.33 87178.33 87164.26 87190.23 87196.27 87202.09 87208.16 87214.25 87220.27 87226.36 87232.40 87238.61 07244.64 87250.71

-0.02 0.12 -0.04 0.02 0.0s 0.06 0.05 0.11 -0.09 -0.04 0.01 -0.03 -0.01 -0.04 0.08 0.01 -0.02

P(J) 86812.50 86908.69 86904.94 86901.09 86897.45 86893,94 86890.36 86886.84 86883.49 86879.80 86016.49 a6073.27 86870.15 86867.00 86863.93 86860.85 06857.92 86854.98 86852.03 86849.09 86846.29 86843.51 86a40.78 86838.12

o-c

LZ:::: 86830.47 86828.02 86825.82 86823.33 86821.10 86818.67r 86816.53

0.16 0.15 0.14 -0.02 -0.02 0.05 0.01 0.01 0.06 -0.26 -0.24 -0.19 -0.08 -0.06 -0.01 -0.02 0.06 0.08 0.04 -0.03 -0.03 -0.05 -0.05 -0.08 -0.06 -0.11 -0.05 -0.05 0.16 0.02 0.10 -0.06 G.01

86810.27 86808.31, 86806.09

0.11 0.17 -0.06

328

EIDEISBERG ET AL. TABLE A.I-Continued 1-2

l-l J

R(J)

0 1

86858.79 86Llb2.86 86866.809 668;i.g

: 4 : i

1: :: 13 :: 16 17 18 :: :: :: 25 26 27

868?8:69 86082.72 86886.68 86890.85s 86895.00 86899.19 E:.:: a6911 :a9 Et:: a6924 a0 86929.01 86933.54 86937.96 86942.45 86946.86

1

86956.23 86960.49 86964.92

0-c -0.11 0.09 0.12 -0.01 0.05 0.07 0.07 -0.05 0.02 0.03 0.06 0.03 0.03 0.08 0.07 0.06 0.05 -0.10 0.04 0.04 0.09 0.03 0.40 0.13 0.01

:: :t 32 :: 35 :; :: 40 41

P(J) 06841.49 86643.691 ab840.261 86836.35~ 86832.961 86829. ia 86825.63% 86822.06 a6aia.67r 86815.07s 86811.741 86808.26¶ 86804.89 86801.56 86798.21

0-c

R(J) 0 1

iS :: :: 23 24 25

L14JJb.L)3 84780.76 84784.66X 84789.01t 04793.4b 84797.61 84802.15 84806.62~ 84611.12 84015.82 84820.59 84025.43 84830.31 84835.32 84840.401 84845.53s 84850.789 84856.11 a4861.52 84866.99 04072.58 a4678.22 64803.94 84889.77 84895.65 84901.59

o c 0.02 -0.03 -0.20 0.00 0.23 0.04 0. lb 0.14 0.12 0.10 0.11 0.12 0.09 0.11 0.10 0.07 0.07 0.08 0.08 0.06 0.09 0.09 0.09 0.10 0.10 0.08

0.02 0.06 -0.04 0.02

86769.76 86166.77 86763.85 8bJbO.90 8bJ57.97 abJ55.07 86752.26 06749.47 86746.58 86143.81 86741.06 96738.30 86735.70 86732.86

-0.10 -0.09 -0.05 -0.05 -0.06 -0.08 -0.02 0.03 -0.04 -0.02 0.00 0.00 0.21 0.02

86127.49 86124.04

0.00 0.01

84165.46 04761.75 %4?50.25* 64754.54s 04751.30 04748.15 04744.95 84741.89r a473a.77 64735.82 64733.01 84730.46r 84?2?.43r 84724.93 84722.40 E::~” 04715.43 04713.34s 04111.22 84709.25 64707 .Oll 84705.51

P(J)

o-c

o-c

0.18

86788.64 86785.36 86782.16 86779.08 i%:E

P(J)

R(J)

0.03 -0.03 0.25 0.01 0.25 0.08 0.10 0.01 0.19 0.05 0.16 0.09 0.09 0.09 0.04

o.na

o-1 J

J

o-c

0.09 0.02 0.06 -0.18 0.03 0.09 0.10 0.15 0.06 0.05 0.09 0.31 -0.04 0.06 0.11 0. lb 0.09 0.06 0.13 0.06 0.11 -0.23 0.09

o-2 J

R(J)

o-c

11 ::

82659.6% 82663.a3¶ 82668.06~ a2672.331 826Jb.JJr a2681.3or 82685.92~ 82690.66~ 82695.53~ a27oo.54r 82705.57~ 82710.79s 82721.48s aZJlb.O%

-0.32 -0.20 -0.11 -0.10 -0.04 -0.01 -0.01 -0.01 0.00 0.03 -0.03 -0.03 -0.13 -0.06

14 15 16 17

82727.001 a2732.69 82738.53 82744.43

-0.18 -0.18 -0.14 -0 16

19

82756.50 82762.90 62769.29 02775.65

-0.28 -0.02 -0.14 -0.28

ia

:i 22

iZ75d;ik Xii

P(J) 82651.91r 02640.53 82644.98 a2641.60 82638.29 82635.12 82632.11 82629.20 82626.61t 62623.7% 82620.971 82618.67s 82616.39 82614.20 82612.25% 82609.86s 82608.34 82607.22r 82604.9Or 82603.50 a2602.52r

0-t -0.43 -0.16

-0.18 -0.15 -0.17 -0.17 -0.14 -0.12 0.00 -0.09 -0.32 :;:;;

-0.15 -0.04 -0.47 -0.1s 0.41 -0.32 -0.27 0.09

1-3 J

R(J) 82651.91~ 82655.57 82659.691 82663.83~ 82668.06~ 82672.33s 82676.JJr 82681.30r a2685.92* 8269O.66r 82695.53x 82700.54, 82705.57~ 82710.79r 82716.09r 82721.48t 82727.00~ 82732.68,

o-c 0. la -0.11 -0.03 -0.05 -0.08 -0.17 -0.16 -0.22 -0.26 -0.29 -0.29 -0.25 -0.28 -0.22 -0.19 -0.16

-E

P(J) 82643.931 82640.36 82636.84 82633.42 82630.07 82626.61~ 82623.751, 82620.971 82617.85 82615.02 82612.25, 82609.86~ 82607.22r 82604.90r 82602.52% 82600.371 82598.28* 82596.331

0-c

-0.21 -0.15 -0.13 -0.13 -0.15 -0.39 -0.13 0.09 -0.12 -0.15 -0.22 -0.01 -0.15 -0.09 -0.18 -0.15 -0.16 -0.13

VACUUM ULTRA-VIOLET SPEmRUM

329

OF CO

TABLE A.I-Continued

b J 0 :

o-o

2-o

R(J)

0-c

90910.20 90913.61 90917.02 9c420.31 90923.58 90926.69 90929.74 90922.79 90935.67 90938.53 90941.26 90944.03

0.16

_ __ _

iJ ::

P(J)

i*E 0:03 0.02 -0.04

ii%.:: 90695:20

-0.02 0.02 0.10 0.00 0.25 0.57

90870.31 90865.87 90861.36

16

0-c

0.03 -0.08 -0.05 -0.06 -0.04 -0.07 -0.04 -0.05 -0.04 -0.01 0.11 0.38 0.01 0.73

J

R(J)

0-c

0

86920.65 06924.35 86928.10 86931.91 86935.73 86939.83 86943.75 06941.86 86951.98 66956.14 86960.42 66964.64 86968.98 86973.26 66977.68 86982.15 66906.64 86991.16 86995.77 87000.36 e7oos.09 87W9.84 87014.51 87019.26 87024.05 87028.92 87033.60 07030.79 87043.07 67040.85 87053.95 87058.96 87064.12 87069.30 07074.19 07079.75 67085.05 87090.35 87095.75 87101.14 87106.57 8711i.02 87117.50 87123.06 87128.66 87134.19 87139.83 67145.45 87151.03 87156.69 87162.53 87157.82 87173.75 87179.61 87185.33 87191.22 87197.08

0.13 0.05 -0.01 -0.06 -0.18 -0.05 -0.14 -0.10 -0.09 :;.O$

: 3 1

1-o

R(J)

J 0

i : 4 5

6 :

9 10 ii :: 14

:: 17

ii

:

88957.6Oa 88961.39 88965.13 86968.80 88972.53 88976.21 88979.86 86983.56 88987.21 ea990.95 88994.54 80990.22 89001.92 89005.53 89009.21 89012.87 89016.50 wn2O. 12 89023.71 89027.44

21

:i%:

:: 24 25

69041.76 89045.35 89048.15

0-c

-0.21 -0.06 -0.03 -0.03 0.02 0.02

_...

“0::: ::ii -0.01 0.00

pJ 0:03 0.03

P(J)

0-c

-0.07 0.05 0.06 0.15 0.22 0.12 0.06

25 26 :;

i*$

0:03 0.01 0.03 0.03 0.03 0.03 0.01 -0.05 -0.33

-Ki

._ :: 45

a903a:19

48 49 :: 52

ii :: __

-0:os -0.01 -0.06 -0.05 -0.02 -0.01 -0.02 0.02 0.00 0.06 0.11 z -0:os -0.05 -0.07 -0.04 0.05 0.01 0.04 -0.07 -0.05 -0.05 -0.06 -0.07 -0.05 -0,on -0.03 -0.03 -0.02 -0.02 -0.02 0.03 0.01 0.05 0.09 0.09 0.02 0.01 0.15 -0.28 -0.08 0.02 -0.04 0.04 0.09

P(J)

0-c

330

EIDELSBERG ET AL. TABLE AI-Continued l-l

R(J)

J

o-c

l-2

f’(J)

o-c

86768.35 86765.62

-0.04 -0.01

86;g.g 06157:Q8 86754.80 86752.10 86749.49 86746.92 66744.38 86741.92 86739.35 86736.81 86734.26 86731.80 86729.46

-0.01 0.04 -0.01 -0.03 -0.08 -0.09 :;.;CI 0:07 0.03 0.01 -0.04 -0.02 0.11

O-l J

R(J)

0-c

23 ::

84824.41 84828.31 84832.37~ a4a36.09t 84840.23r 84842.741 8484a.90r 84653.02 84857.39 84861. a2 84866.38 84870.95 84875.59 uaao. 43 84885.20 84890.19 81895.24 84900.28 84905.42 84916.71 a4916.08 84921.38 84926.80 84932.39 84943.63 84936.00

-0.04 0.06 0.22 -0.02 0.06 0.44 0.39 0.21 0.21 0.18 0.21 0.17 0.11 0.1s 0.10 0.17 0.20 0.17 0.14 OI20 0.25 0.17 0.11 0.17 0.30 0.16

26

84949.20

-0.01

6 7

::

P(J)

o_c

a4a17.3at 04814.06r 84810.29

0.30 0.54 0.25

a4803.54 84800.27 84797.07 84794.12 a4791. lot 84788.11 84785.27 84782.59 84779.9ar 84776.17s 04774.85 84772.51 a4770.07r 84767.88 84765.83 84763.57s 84761.59 84760.11

0.21 0.17 0.12 0.23 0.21 0.11 0.10 0.15 0.20 -0.04 0.12 0.19 0.07 0.12 0.23 0.05 0.06 0.50

84754.30¶ a4956.21

-0.07 0.17

R(J)

J

o-c

0

y4:.:g9

:

8479a:73

0

82753.06~

:

82761.141 82757.03r

: :

a2765.25t 82769.461 82773.79r 82778.23r 82782.75s 82?87.40* 82792.18 82797.001 82801.98~ a2807. 82812.16s 82817.48~ 82822.71; 82828.34s 82834.24~ 82839.99r 82845.84

t 9 :: 12 13 14 ii :; 18 19 m

P(J)

o-c

_;.g

cm

0: 19

-0.64 -0.50 -0.35 -0.31 -0.28 -0.25 -0.22 -0.22 -0.21 -0.18 -0.22 -0.21 -0.28 -0.32 -0.30 -0.46 -0.39 -0.13 -0.12 -0.14

94?79.9&

-0.17

82746.35 ::::::; 82731.07 82732.93 82729.89 82726.99 82724.39~ 82721.551 a271a.72r w;~.;; 82712: 19 82710.07 82707.66X 82705.78 82701.16 82702.71r 82699.64

-0.15 -0.12 0.08 -0.07 -0.32 -0.15 -0.00 -0. la 0.00 -0.24 -0.24 -0.10 0.11 0.00

l-3

R(J)

J 0

i 9 j

4 5

82745.37 82749.08 82753.06t 82757.03r 82761.141 82765.32, a2?69.46* 82773.79s 82778.231 82782.75r a2787.40* 82792.18s 82797.00t 82aoi.9ar 82807.00* 82812.16r 82817.48, 92922.74, 82928.341

o-c -0.11 -0.19 -0.09 -0.08 -0.04 -0.03 -0.15 -0.18 -0.19 -0.22 -0.23 -0.19 -0.20 -0.15 -0.16 -0.12 -0.01 -O.US 0.15

P(J)

o-c

82738.07 82734.64 82731.16 82727.90

-0.17 -0.12 -0.20 -0.20

82715.83 82713.02 82710.07t 82707.66~ 82705.27 82702.71r a2700.w 82698.26, 82696.21, a2694.20r 92692.3Or B269o.571 82668.84

-0.13 -0.15 -0.41 -0.23 -0.13 -0.30 -0.11 -0.25 -0.20 -0.21 -0.21 -0.12 -0.14

VACUUM ULTRA-VIOLET SPECTRUM OF CO

331

TABLE A.I-Continued C

J

2-O

R(J)

o-c

c%~~~ 90909: 70 90912.97

fom;.;; 90922h 90925.39

E:::: 90933.86

13 14 is 16

EZ 90942:00

0.05 0.03 0.07 0.01 0.02 -0.07 -0.02 -0.02 -0.03 0.02 0.01 0.10 0.24 0.51

o-o P(J)

o_

90895.55 90891.76

0.06 0.02 0.01 0.02 -0.03

EE: 90879:98 90875.86 90871.73 90867.48 90863.14 %a%.73 vBv54.22 !E-E 90840:38 90835.92 90830.46

-0.07 -0.03 -0.04 -0.04 -0.04 -0.05 -0.04 0.04 0.11 0.49 -0.05

0

9 :: 12 :: :: 17 18 :; 21 22 :: 25 26 27 28

R(J) 88953.91 88957.54 88961.19 88964.89 8818.50 88972.19 88975.82 88979.47 88983.12 88986.83 88990.48 88994.13 88997.78 89001.42 89005.05 89008.69 89012.32 89015.94 89019.56 89023.17 89026.78 89030.37 89033.96 89037.55 89040.67 89044.43 89048.08 89051.81 89055.55

0-c

0.01 -0.02 -0.04 0.00 -0.05 -0.02 -0.04 -0.06 -0.06 0.01 0.03 0.02 0.01 0.04 :z -0:01 -0.01 0.03 -0.01 -0.01 -0.06 0.02 -0.11 -0.45 -0.25 -0.16 0.03 0.25

0 1 : 4 c

i

7 8 1: :: :: 15 :; 18 19

1-o

J

J

p(J)

io 21 0-c

22 23

ii 88946.56 88942.95 88939.27 88935.63 88931.93 86928.24 88924.63 86920.94 88917.33 88913.64 68909.99 88906.34 88902.67 86899.01 ea895.39 66891.69 88668.02 88684.46 66880.73 68877.02 88073.43 88869.79 68866.22 88862.55

-0.02 0.03 0.02 0.03 0.01 -0.03 0.02 -0.01 0.03 0.00 0.01 0.01 -0.08 -0.01 0.04 -0.01 -0.02 0.07 -0.01 -0.06 -0.02 0.04 0.13 0.13

25 26 :; 29 30

R(J) 86920.09 86923.90 86927.73 86931.56 86935.53 86939.60 86943.43 86947.49 86951.59 86955.76 86959.98 669%. 16 86968.44 86972.78 86977.14 86981.57 86986.01 869%. 52 86995.10 86999.71 87004.31 87009.00 87013.71 87018.44 87023.30 87028.17 87033.04 87037.97 Ex 87052:85

o-c -0.04 0.01 0.03 0.01 0.07 0.11 0.01 0.03 0.03 0.05 E 0:02 0.03 0.01 0.03 0.01 0.01 0.03 i:C 0.01 0.00 -0.03 0.02 0.05 0.03 0.03 0.10 -E

P(J)

86912.68 86909.06 86905.57 86902.05 %8;i.:; 8689l:80 06888.48 86885.22 86881.98 86878.79 86875.74 66872.80 86869.69 86866.66 86863.80 86860.86 86858.02 86655.21 86852.57 86849.89 p84:.;; 86842:16 86839.67 86837.22 86834.77 86832.47 86830.21

o-c -0.07 -0.08 -0.02 -0.02 0.00 -0.07 -0.02 -0.03 -0.02 -0.05 -0.07 0.01 0.12 0.03 0.03 0.03 -0.04 -0.08 -0.07 -0.01 -0.02 -0.02 -0.01 -0.01 -0.02 -0.03 -0.10 -0.05 -0.02

EIDELSBERG ET AL.

332

TABLE AI-Continued 2-o

d J

R(J)

o_c

o-o P(J)

o_c

J 0 1

.E:.:: W792:55

9Q647.73 90650.46

-0.17 0.02

0.59 0.25 0.05 -E -0:OS -0.03

90772.01 W767.71 z: 90763.22 A 0’01

__._.

1-o J

R(J)

0

66906.26 66911.62 66915.33 88918.60 66922.25 66925.62 66929.16

-0.03 0.02 0.03

66953.61

-0.01

88964.32 f8;;;.;;

0.02 1t.s

1

i

3

28974179

o_c

-E -0.16 -0.15

0:05

P(J)

o_c

686L74.13* 66660.541 66677.M) 66673.43 66859.97 66666.45 m863.04 69859.50 68656.14 66652.64

0.24 0.13 0.07 -0.02 -0.01 -0.06 0.00 -0.07 0.04 -0.01

____.

0.02 -0.06 0.12 0.03 -0.05 -0.04 0.05

______

zz: 66642.16 98636.92 66635.37 66631.63’ 86628.39 68625.04

R(J)

o_c

zz:: 1:::: m9ze: 104 66931.91r 66935.73r 1939.57s 66943.6% 26947.06 Ia:; 6695i61

:z 0:22 0.30 0.60

:*i: 0:01

E:*t 66971:03 66975.26 96979.44

:*zY 0:12 -0.04 0.01 -0.02

fmg.; 66992:36 66996.71

-0.05 0.01 -0.02 -0.05

P(J) 66913.71 66910.30

o_c

Ez! 66900:27

-0.14 -0.10 -0.02 -0.06 0.07

EE.:: 666QO:66 86667.59 maw.59 66661.71 66670.794 66676.77r 66672.754 86669.61r 66865.651

-E -0:03 -0.01 0.06 0.20 0.25 0.15 0.01 -0.09 -0.27

VACUUM ULTRA-VIOLET

333

SPECTRUM OF CO

TABLE A.11 Observed Term Values (in cm-‘) for the o = 0, 1, and 2 Levels of the B’E+ State of CO

J

V=O

v=

E:.::

1

v-2

89990.24

0

i :

s::.::

sz: MJ21:U

iK:: B699e: ::::E .9;9i ;;

J

a7173:14 87219.92 a7270.52 :;:::$! 87445: 60 87511.73 87581.68 87655.49 07133.20 87814.77 a7900.21 ~~~:~ xl: SE::

::

:Z:Z 89727.51 kx a99& 90 90057.w 90148.92 90214.69 9o344.% 90147.10

:Z%: 09788.74 89938.69 9oo92.81 90250.74 ~:::~:: 90746:87 90919.81 91096.39 91276.73 91460.76 91648.63 91839.90 92035.07 92233.93 92436.38 92642.50 92852.34 93065.59 93282.69 93503.44 93727.71 93955.65 91107.14 94422.37 94660.99 94903.20

ii ::

22 23 Is 26 27 28 29

JO

z:.;; aBa42:07 88965.76 89093.58 a9224 * 97 89360.19

::

91695.96 91978.57 92130.45

v= 1 88951.06 W57.72 w965.13 W976.24

:%i

~~:::x %::z 86991197 81020.99 87050.77 87084.25 87121.41 87162.43

01

91093.19 91123.18 91156.99 91194.59 91235.82 titBO.59 91328.63 913a3.12 91439.22 91499. a9 9iMiito 91630.47 91701.42 91776.22 91854.03

v=o

33 34 35 36 37 :: 4” ii 42 13

u

:z 47

ir! 49 50 51 :: 54 55 56 57

!E:: B?30?:61 87363.49 87422.99 B74a6.13 07553.02 87623.62 87697.93 07775.94 87857.65 07942.90 Es:;: ~:K: W25:Ol 88532.62 EEz Bae?6:?2 aa998.70 z:::-:: p;m& a%63.50 09807.36 89954.78 90105.82 90260.44 9O418.67 90580.52 90745.05 90914.87 91087.42 91263.49 91443.06 91626.21 91813.07 92002. 92196.82 92394.19 92594.9D 92799.25 93007.06

a7

!K:: 89196:66 892bO.74 89288.50 a9339.87 EE:::: h%d::Z 89651.58 89725.06 EE 89966177 90054.61 90146.11

v=2 90906.49

E%

9V92?:96 9094a.31 Es 91oo6: 93 :E:.z 9llO3:B9 91143.3B 91la6.55 pg.:; 9133?:72

EIDELSBERG ET AL.

334

TABLE A.II-Continued 12p. J

v=o

1927.55 LE:: : 86972.09 %E ll7049:99 87083.35 87120.44 87160.58 87205.80 07253.94 07305.84 87361.39 87420.69 87483.62 87550.28 87620.65 87694.68 87772.34 67853.73 67938.76 00027.45 88119.86 88215.89 88315.61 80418.99 08527.09 88636.73 88750.86

13p. v= 1 88950.22 88953.92 88961.22 88972.21 88986.85 fl9005.12 :::::.:: 89082:02 89114.95 89151.58 89191.84 89235.73 89283.28 89334.51 89389.31 88%: 09575:71 09645.12 89718.14 a9794.80 a9075.04 89959.03 90046.44 90137.26 90232.22 90330.69 90432.86 90538.65 90648.10

v=2 90899.21 90902.76 90909.90 90920.66 90934.92 90952.79 90974.23 90999.29 91027.90 91060.08 91095.85 51135.18 91178.15 91224.71 91275.05 91328.06

J

v=o

0

86917.20

i 2

lE% 86938: 52 86952.65 i%.:: 87016:71 %x! 87112:05 Kz 07239:30 :::zt 87390:20 07450.32 07521.94 K!%

v= 1

ZE

88925:e1 iE~:: 00970:31 i%E mO62:01 89996.88 89135.36 89177.17 89222.66 tK:ii 89379:66 89438.91 89501.74 89567.93 89637.64 89710.79 09787.64

v=2

VACUUM ULTRA-VIOLET

SPECTRUM OF CO

335

TABLE A.111 Calculated Term Values (in cm-‘) for the D = 0 and 1 Levels of the B’Z+ State of i4CL60 14c160

J 0 : : 5 ; 8

1: 11 :: 14 :: 17 18 :i 21 22 :: :i :iG 29 30 :: :: :z :; 39 :; 42 :: 45 46

v=o 86916.98 86920.06 86927.71 86938.45 86952.76 86970.65 86992.12 87017.17 87045.79 87071.90 87113.75 87153.09 87195.99 87242.47 87292.51 67346.12 07403.29 07464.02 87528.31 87596.15 87667.55 87742.49 87820.98 87903.02 87990.60 80077.72 88170.37 88266.55 88366.26 88469.49 88576.24 88686.51 88800.28 88917.57 89038.35 89162.64 89290.41 89421.68 89556.42 89694.64 89836.34 89981.50 90130.12 90282.20 90437.73 90596.70 90759.11

v=l 88915.35 88918.88 88925.95 88936.55 E: i: 86989.53 89014.25 89042.49 89074.21 89109.57 89148.40 89190.75 89236.62 89286.01 89320.92 89395.34 89455.28 89518.72 89585.67 89656.13 89730.09 89807.55 89888.50 89972.95 90060.88 90152.30 90247.20 90345.57 90447.42 90552.74 90661.52 90773.76 90889.46 91008.61 91131.20 91257.23 91386.69 91519.59 91655.91 91795.64 91938.79 92085.35 92235.30 923138.65 92545.38 92705.49

ACKNOWLEDGMENTS We thank Frangois Rostas for many useful contributions and a critical reading of the manuscript. Thanks are also due to Helene Lefebvre-Brion for helpful counseling on the pmdimocmtion problems encountered in this work. The able help of Maurice Benharrous with the experiments and of Sylvie Gordon with the preparation of the manuscript is gratefully acknowledged. RECEIVED:

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336

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