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Doppler-limited dye laser excitation spectroscopy of the HSO radical
JOURNAL
OF
MOLECULAR
SPECTROSCOPY
Doppler-Limited
(1980)
80,334-350
Dye Laser Excitation the HSO Radical
Spectroscopy
of
MASAO KAKIMOTO, SHUJI SAITO, AND EIZI HIROTA Institute for Molecular
Science,
Okazaki 444, Japan
The cw dye laser excitation spectrum of the A *A’(OO3)t d zA”(OOO)vihronic transition of the HSO radical was observed between 16 420 and 16 520 cm-r with Doppler-limited resolutjon, 0.03 cm-‘. The HSO radical was produced by reaction of discharged oxygen with H,S or CH,SH. The observed spectra were assigned to 751 transitions of the K: c K6;=2+3, 1+2,0+-l, 1+0,2+1,and3 + 2 subbands, and were analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation interaction constants with good precision. The signs of the spin-rotation interaction constants were determined for both the upper and the lower state from the observed spectra. The band origin obtained is 16 483.0252 (2.5~ = 0.0013) cm-r. The molecular constants which were determined reproduce the observed transitions with an average deviation of 0.0045 cm-l. INTRODUCTION
The HSO radical has been the subject of various discussions. From reaction kinetics studies (I -3), HSO is expected to play an important role in various oxidation reactions of hydrogen sulfide or mercaptans, whose mechanisms are not fully understood because of the complexity arising from the tendency of the sulfur atom to form hydrogen- and oxygen-containing intermediates of varying structure and composition. Slagle et al. (I), on the basis of a reaction kinetics study with crossed jets, suggested the formation of HSO in reactions of various mercaptans with atomic oxygen. Schurath et al. (2) observed chemiluminescence spectra emitted in the reaction system of H,S (or D2S), atomic oxygen, and OS, and concluded that the spectra they observed were due to HSO (or DSO) through vibrational analyses of both the HSO and the DSO spectra and through a molecular structure determination by means of band-contour simulation of one of the HSO bands. These experimental findings stimulated an ab initio calculation study (4) on this new radical to predict such properties as the geometry, the dipole moment, and the vibrational frequencies. The HSO radical is interesting also from a spectroscopic viewpoint because of its similarity in molecular structure of the HOz radical, which has been studied extensively by far-infrared (5, 6) and infrared (7,8) laser magnetic resonance, microwave absorption (9-12), and near-infrared emission (13) spectroscopy. No high-resolution spectroscopy on the HSO radical has, however, been reported in any frequency region, and nothing is known accurately about the geometry or the vibrational frequencies of this radical in the ground or in any excited electronic state. The present paper is concerned with the first high-resolution study of the HSO radical, and presents precise molecular constants for both the lowest excited and 0022-2852/80/040334-17$02.00/0 Copyright All rights
0 1980 by Academic of reproduction
Press.
in any form
Inc. reserved.
334
DYE LASER SPECTROSCOPY
OF HSO
335
FIG. 1. Block diagram of the laser excitation spectrometer. BSI through BS3 are Pyrex glass beam splitters, Ml through M3 are 100% reflection mirrors, F stands for optical filters (Hoya R62), L for a lens system, and PM1 and PM2 denote photomultipliers (HTV R666S). ET. 1 is a piezo-mounted confocal etalon of FSR 2 GHz, driven by a high-voltage saw tooth, and used as a spectrum analyzer. ET. 2 is a temperature-stabilized confocal etalon of FSR 1.5 GHz. PDl and PD2 are silicon photodiodes.
the ground electronic states, determined from a rotational analysis of a cw dye laser excitation spectrum in the visible region. The resolution of the present method is entirely limited by the Doppler width of the HSO radical, 0.9 GHz. EXPERIMENTAL
DETAILS
The experimental arrangement is shown schematically in Fig. 1. The fluorescence cell was made of a Pyrex glass tube 35 mm in outer diameter and 600 mm long, sealed with a Pyrex glass Brewster-angle window at each end. A few tens of watts, 2450-MHz microwave discharge cavity was placed about 40 cm upstream of the cell. The discharged products and the reactant were introduced into the cell through the inner and outer coaxial tubes of a side arm, were mixed right at the entrance to the cell, and were pumped out continuously from the cell by a mechanical booster pump followed by a rotary pump. The linear flow speed was estimated to be about 20 m/set at 100 mTorr. The dye laser beam, collimated to about 1.5 mm diameter, entered and left the cell through the Brewster-angle windows. A photomultiplier (HTV R666S) was placed about 5 cm downstream from the mixing point, and the fluorescence light was collected through the wall of the cell withf - ‘/2 optics (L in Fig. 1). The scattered light was reduced by light baffles inside the cell and was blocked by four sheets of Hoya R62 edge filters (cutting off h < 620 nm) in front of the photomultiplier. The laser beam was mechanically chopped at 1.65 kHz and the signal from the photomultiplier was detected by a lock-in amplifier (PAR 124A) operated at the same frequency.
336
KAKIMOTO,
SAITO, AND HIROTA
616'606
'51.1Le'~0,1L
n
132.12-13112
I
I
I
I
.8
16487.0
.2
.c
cm-’
FIG. 2. An
example of excitation spectra. The upper trace is the excitation spectrum of HSO A 2A’(O03) +- J? *A”(OOO)and the lower trace is the iodine excitation spectrum with frequency marker (1.5~GHz separation). Reaction pressures were 0, 18 mTorr and H,S 70 mTorr, and the laser power was about 80 mW.
A dye laser (Coherent Radiation Model 599) was pumped by 5 to 6 W output from an argon ion laser (Spectra Physics Model 171-05) in the all-line operating mode. The dye laser was operated in single mode with Rhodamine 6G as the lasing dye. The dye laser output power (measured after Ml in Fig. 1) varied from 80 to 40 mW, as the thin etalon in the laser cavity was tilted to tune the laser frequency. The dye laser linewidth was not directly measured, but was found to be less than the bandpass of the spectrum analyzer monitoring the laser mode, i.e., less than 6 MHz. This enabled us to observe Doppler-limited spectra in the visible region. In fact, the observed widths of the HSO lines agreed well with the calculated Doppler width, 0.9 GHz fwhm. A single scan of the dye laser covered about 29 GHz, and two successive scans were shifted by 10 GHz in frequency, so that each HSO line was observed at least twice, and usually three times. An g5-cm double monochromator (Spex 14018) was used to roughly locate the dye laser wavenumber. The precise wavenumber measurement was done in the following way (see Fig. 1). A part (-8%) of the dye laser output was diverted from the main beam going to the cell by a Pyrex glass beam splitter BSl, and was further divided into three parts by Pyrex glass beam splitters BS2 and BS3. The first part (from BS2) was used to monitor the dye laser mode by means of a spectrum analyzer ET. 1 (FSR 2 GHz). The second part (from BS3) went into a temperature-stabilized etalon ET. 2 (FSR 1.5 GHz), whose fringes were used as frequency markers. The last part of the dye laser beam passed through a glass cell filled with IZat the saturated vapor pressure. The excitation spectrum of IZ and the superimposed frequency markers coming from ET. 2 were recorded at the same time as the HSO excitation spectrum on a two-pen strip chart recorder. A typical example of the recorder trace
337
DYELASERSPECTROSCOPYOFHSO N=9
/
I
I
we70
16465
'
cm
-1
FIG. 3. A part of the HSO excitation
spectrum. Assignments are indicated only forPQ,,PRI, ‘Qn, and but most of the remaining lines are also assigned (see Table Al). The lower trace is excitation spectrum.
rRR, transitions, the iodine
is shown in Fig. 2. The wavenumbers of the I, lines have been measured precisely (with a precision of 10m3to lo4 cm-‘) by Gerstenkorn and Luc (14), and these were used as the standards to measure the wavenumbers of HSO lines. The maximum deviation among wavenumber determinations for a single line from several scans was about 0.003 cm-’ in most cases. To optimize radical generation we tuned the dye laser to about 16 480 cm-‘, which, according to Schurath et al. (2), corresponds to the peak of the A 2A’(O03)+= d 2A"(OOO) band of HSO, and we monitored the strength of the fluorescence signal for several chemical reactions. We found that the reactions
(02)disch + CHsSH
(1)
(Q)disch + H2S
(2)
and gave the same fluorescence excitation spectrum in this region with good S/N ratio. The best S/N ratio was obtained when the CH,SH or H,S pressure was high enough, as compared to that of 02, to quench the SO, chemiluminescence, but the total pressure was not too high. Typical partial pressures used were 18 and 22 mTorr, respectively, for 0, and CH,SH in reaction (1) and 10 and 40 mTorr, respectively, for 0, and H,S in reaction (2), although optimum conditions seemed to depend on the immediate past history of the cell, the pumping speed, and the distance between the mixing point and the observation point. Reaction (2) was used for subsequent observations. We initially concluded that the spectrum we observed was due to HSO because reactions (1) and (2) gave identical spectra, and the position of the spectrum agreed with that of Schurath et al. (2). This initial assumption was fully supported by all of the spectroscopic constants deduced from an analysis of the high-resolution spectrum. The spectral region studied extends from 16 420 to 16 520 cm-‘. The PSD time constant used was 1 set and the scan rate was about 1 GHzllS sec. ROTATIONAL
ANALYSIS
In this work we adopt the vibronic assignment of Schurath et al. (2). The observed spectrum thus corresponds to the A 2A‘(003) + J%2A"(OOO) vibronic band,
338
KAKIMOTO,
SAITO,
AND
HIROTA
and rovibronic transitions accordingly obey c-type selection rules. Figure 3 shows a part of the spectrum. As seen in the figure, two series of strong lines can easily be recognized, which we assigned to the Q branches of the K; t K’; = 1 t 0 and 0 t 1 subbands, respectively, since neither series shows K-type doubling. Another series of fairly strong lines, which is only barely seen in Fig. 3 but is more prominent in the higher-wavenumber region, was also picked out and was assigned to the R branch of the Kh t Kz = 1 t 0 subband. It was found that the K, assignment of Schurath et al. (2) should be shifted by one unit, i.e., their K; + Kg = I + 0, 2 + 1, 3 + 2 should be replaced by KL + Kg = 0 + 1, 1 -+ 0, 2 + 1. This reassignment is based on our observation of the K-type doubling for the Kh t K; = 2 + 1 subband. Spin splittings were observed in the rR,, transitions and in the low-N transitions of the rQOand PQ1 branches: the spin splitting of the Q branches becomes smaller as N increases and eventually the two components overlap each other within the Doppler width, as shown in Fig. 3. From the N assignment of these three branches alone, a fairly good set of rotational constants and spin-rotation interaction constants was obtained to start with, except that the ground-state A value was fixed to that calculated from the molecular structure of Schurath et al. (2). The assigned lines were analyzed by the method of least squares and the parameters thus obtained were in turn used to assign other lines with higher N and/or K, values. This cycle of least-squares fit and assignment of lines was repeated; the number of adjustable parameters was increased gradually as more lines were assigned. The signs of the spin-rotation interaction constants, the E,,‘s, were determined in the following way. Among the four possible sign combinations, (e&,&J = (+,+), (-,-), (+,-), and{-,+), the first twocombinations, (+,+) and (-,-), were easily eliminated by using the observed line frequencies of four branches, PQI,TQ,,, rR,,, and ‘Q1. In order to discriminate between the two remaining cases, (e&&J = (+ , -) and (- , +), it was necessary to observe the rather weak transitions with N 5 3. The case of 'R,,(O) is shown in Fig. 4 as an example. As seen in a
I
I
I I I
I
.a
I 16L93.0
I I I
I
I
.2
.L
I
.6 cm-’
FIG. 4. The excitation spectrum of HSO around l,, c O,O. Vertical lines indicate the calculated spectra. Stronger lines areJ’ cJ” = S/Zt 1%and weaker IinesJ’ +-J” = 44 + %. Solid lines corre) = (-,+). (The assignment of other lines is a: spond to (&,E:.) = (+,-) and broken lines to (EL, C” (111 llL10 + 100,10, b: 173.14 + 172,,6, c: 123.,0 + 132,12r and d: 11~ +- 11~~0.)
DYE LASER SPECTROSCOPY
OF HSO
339
the figure, only the (e&e&) = (+ ,-) sign combination reproduces the observed spectral pattern in both the line position and the relative intensity. Thus we have determined experimentally that E,, is positive in the A *A ’ state and is negative in the x 2A” state. The following Hamiltonian was used in the analysis: H = Hot + & H,,, = AN;
(3)
+ I-L
+ BN; + CNf,
(4)
Hcd = -AN(N2)* - ANKNIN: - AKN; - 2S,N’(N”, - Nf)
- &{(N; H,, = l,,N,S,
+
EbbNbSb
+
- N2,)N2, + N2,(N; - Nf)},
(5) (6)
G,NJ,
for both the upper and the lower states, where the notation follows that of Bowater et ai. (15). It was found to be unnecessary to include higher-order terms in the centrifugal distortion Hamiltonian, I&,. The effect of centrifugal distortion terms in the spin-rotation interaction was examined, but these did not improve the fit at all. The energy matrix was set up with Wang-type symmetric-top wavefunctions as bases, where all matrix elements of the type AJ = 0, AN = 0, -+l, and AK, = 0, k2 were included, and was diagonalized to give the energy eigenvalues. In this way, 646 of 781 observed lines were assigned to 751 transitions. The subbands studied are summarized in Table I and all the assigned transitions are listed in Table Al of the Appendix. Most of the observed lines which remain unassigned are higher- or lower-N transitions of the subbands listed in Table I or high-N TABLE 1 Studied Subbands of HSO A ‘A ‘(003) 6 $? *A”(OOO)
Ka’ + Ka" 2
+
3
1+2
0
-1
1+
0
transitions
a
(Ib
P(3) Q(3) R(8)
-
P(6) Q(l0) R(15)
16 23 29
P(2) Q(2) R(7)
-
P(12) Q(16) R(22)
34 48 51
P(1) Q(l) R(1)
-
P(15) Q(21) R(24)
29 40 46
P(Z) Q(1) R(O)
-
P(20) Q(23) R(25)
35 44 51
P(7) Q(3) R(3)
-
P(21) Q(24) R(22)
49 81 74
P(12) Q(9) R(15)
-
P(18) Q(23) R(21)
21 57 23
2
-1
3
f
a
Minimum and maximum N values are indicated in parentheses.
b
Number of transitions used in the least-squares fit.
2
340
KAKIMOTO,
SAITO, AND HIROTA
transitions of the KA + Kz = 4 + 3 subband. These lines were, however, not included in the analysis since they were usually too weak or too heavily overlapped. Even among those assigned lines listed in Table I or Table Al, it often happened that more than one transition had to be assigned to the same observed line. When the overlapping resulted in shoulders or broadening of lines and thus made wavenumber measurement inaccurate or even impossible, these lines were not included in the least-squares fit. In Table Al the calculated wavenumbers, rather than the observed wavenumbers, are listed for these transitions in parentheses. On the other hand, in the case of exact coincidence of two or more transitions within the Doppler width, which did not cause any apparent shoulder or broadening, these blended lines were included in the least-squares analysis. All the lines used in the least-squares fit were given the same weight, irrespective of their intensity or multiple assignment. The molecular constants determined for the excited and the ground states are listed in Table II. The rms deviation between the observed and the calculated wavenumbers is 0.0045 cm-‘, which is only slightly larger than one-tenth of the Doppler width, 0.9 GHz or 0.03 cm-‘. No evidence of perturbation in the excited state was observed. DISCUSSION
Dye laser excitation spectroscopy, which was utilized in the present work, enables us to achieve very high sensitivity and very high resolution. The resolution is entirely Doppler limited and is nearly 10 times better than that of conventional high-resolution spectroscopy. As a result we were able to determine the molecular constants of the HSO radical in both the A *A'(OO3) and the J? *A"(OOO) states with high precision. The band origin we obtained, 16 483.0252 (13) cm-*, TABLE II Molecular Constants of HSO (MHz)
constant
; *A"(OOO)
A %'(003) 291 862(16)
A
299 478(20)
B
16 934.7(17)
20 504.4(17)
C
15 802.1(17)
19 135.6(17) 0.0318(25)
0.0483(22)
0.857(58)
3.318(38)
27.2(20)
39.9(18)
E
0.00506(58)
0.00202(56)
4.01(41)
0.45(38)
17 854(165)
aa
Ebb E cc
-433(32)
-352(32)
-5(32)
VO a
in cm
Numbers standard digits.
-1
-10 292(64)
87(32)
= 16 483.0252U31a
.
in parentheses deviation
are 2.5 times
and apply
the
to the last
DYELASERSPECTROSCOPYOFHSO
341
is 21 cm-’ higher than that of Schurath et al. (2), 16 462 cm-‘. This difference is entirely due to their improper assignment of the K, values. In a subsequent paper (16), the present results will be combined with those for DSO, for which excitation spectra are now being analyzed, to provide more information on the molecular structure and force field. The sign of the ground-state spin-rotation interaction constant, E:,, can be estimated from the theoretical expression (17), I, 2 I(OIL&z) I’/(& - E,,). (7) %l = -4A.ASo 11
If, as a first approximation, we assume that (a) only the A 2A’ state makes a dominant contribution to the sum in Eq. (7), (b) I (2 IL, IA > I 2 is unity, and (c) the spin-orbit coupling constant As0 is equal to that obtained from the ground-state spin splitting of the neutral sulfur atom, As0 = - 177 cm-’ (18), then e& is calculated to be -0.43 cm-’ or -13 GHz. This calculation supports the sign of &, determined in the present work. A negative E:, is also supported by the extremely well determined (I 1) negative value of &, for the HO, radical, whose electron configuration is similar to that of HSO. As already mentioned, Schurath et al. (2) used the following reaction system to observe the chemiluminescence of the HSO radical: H2S + (02)disch + 0,.
(8)
Their thermochemical argument suggests that ozone is required for the production of the HSO radical, especially in its electronically excited states. The reaction mechanism they proposed is the well-established initial oxidation of H,S: H,S + 0 + SH + OH
(9)
SH + 0, + HSO* + 0,.
(10)
followed by We, on the other hand, did not use ozone because we wished to avoid strong chemiluminescence, but we were still able to observe the HSO spectrum with the reaction (2). This means that the reaction route, H,S + 0 -+ HSO + H,
(11)
might be responsible for the production of HSO. But the question then arises why reaction (1 l), which seems to be endothermic, can compete with an exothermic route, reaction (9). One possibility is, as Slagle et al. (29) mentioned, that reaction (11) might be slightly exothermic. Another possibility is the presence of a small amount of 0, formed by microwave discharge in 02, which allows route (10) to take place, although the production of O3 from atomic oxygen and molecular oxygen requires a third body, that is, high pressure. The information established in the present paper should be useful in kinetics studies spectroscopically monitoring the concentration of HSO as an intermediate. APPENDIX
Table Al lists the observed transitions of HSO A 2A’(O03) +- 2 “A”(OO0). Wavenumbers in parentheses are calculated values. An asterisk indicates a line assigned more than once. 0 - C stands for 1O+3times the observed wavenumber minus the calculated wavenumber.
P2
:
:
: 2
3 :
:
:
:
: 2
2 2
: 2 2
:
:
:
:1
: 3
:
: 2
: 1
:
:.: 4’5 5’5 a:5
:,: 2’5 5:s 2.5 45 1’5 415
2.5
1:s
15
9
8 :
:
: , 1 , , i:: :*: a:5
: 6
8.5
,,5
515 L’5
5’5 415 b5 5’5
3.5 :*:
.3.5 :5
2:5 3 5
J
: b
0
3
:
:
2 :
:
:
3
3 3 :
3 3
:
:
r(c
LWEP
:
l.
:
5 5 :
. :
a
:
II
TABLE Al
04-1
1.221) ,..22 1.575
8;787
‘~052~ ,908. ‘~8521 .9Cd* .409*
16437.70, 437.008 437.L61 437.Ob4 *,6.70,* 436.165
16.3
164,1,P5,” 4,0.11,* 431,953” *,0.113* 429.767+ 428..R21 .29.767” .28.482* 427..,1* 426..O,r 42?.*31r *21.40,+ .24.888. .2**019* l2*.%5c,* .2*.019*
OBS.
1 :
3 : :
6 -7 :i -14 -9 -11 7 -*
: -8
2 1 -3
5 1
: :
: :
:
7
7 :
:76:5
i
:
:
: :
:
:
i
1
:
:
t
:
:
-5
i
: 1
1 :
P
: 2 2 2
:
: 2
:: 15 16 16 16 16
:
:
:
: 2
:
: 2
2 2
;
: 6
:
:
:
:
:
:
0 1
0
ICC.
UPPER
14 I5
**
::
::
:: 12 1, 13
:: 11 11 12
10 10
N
:
-2 -2 -3 4 3 1 -1
2
3
: 5 -1 -6 3 -2
:
0 -5
-:
5
:
O-C
List of Transitions of HSO A *A’(OO3)t_??
15
;;:
:s 5.5 6.5 5.5 715
:::
::: 4.5 3’5 4.5 315 5.5
0.5 1:5
: B2
i
7
:
: :
:
: :
t
: 3 3
2
2
:
:: 15 15 15 15
14
f;;;
14:5 Ill.5 15.5 16.5 15.5
ii
1, 13 ::
::
11
:: 10 10 ::
:
N
13:5 ::*: 12.5 IC.5 13.5 11.5 11.5 15.5
::*: 11:5
10.5 9.5 11.5 10.5 11.5 10;5 12.5
,
*A”(OOO)
:
:
:
:
: 2
: :
2
:
: :
:
:
2
3
: :
:
3 3 3 ,
:3 :
: 3
:
:
:
3
:
6 6
2
:
:
: :
: :
:
: :
1
T
O
13
:: ::
::
10 11 1, ii
10 9 ::
8 9 9 9
:
7 7 7 :
I(c
LOWER 1(1
,
z:: 7;5 B 5 715
:,: 6’5 715
4.5 3:s 5-5 6’5 5:5 6.5 6.5 5’5 6:5
t*: 3’5
3:s 2’5
35 1.5
:::
2.5
14.5
:::: ::::
::::
i4:5
12:5 ;;::
11.5 12.5 ::*:
10:5 11.5 10.5 12.5
,x
0.5 8.5 10.5 ,z
b20,OPP 427;961 427.717 426.022 425,663 .25.687 625.326
412,217. 431,925) 431.71)b 430. .74 630.058 l30.27, .29.869 .~~ 428.150,
.3,.92,, 5,,.564 43,..55 432.362
,
I
,
::x .4e: ,66 445.9591 4.5.9.5e.r 445.612) ‘43.P62 4.3.603 44,.,8&l 4*3.oao 441.34, ll .025) 450.5L4 wo.291 4,8.502r 43e;222 437.500 .,7.249
1 b452.+22* 651 ..OO* 452.301 l51.,(1,, I +50,500> 4CP.P4, l50 ..6., 449.846 4.m.571, I 4be,ooo)
I
,
,
CM-,
16.,6.652 436.103N l,5.401* *,..975 .,5. ,97* *,4 ; 094 4,6,028
OBS.
1
2 -1 -15 -1 -4 2
-: -7 -1 1
1
-i -1
-5 6 -1
* -4 3
Y 3 2 3 -1 3
: 2
2 4 1
-5 -3
-: -6 -6 -I
:
O-C
R e
9
9 10 10 10 10
: :
*
: 2 z 2
2
10 10
::
:: 11 ::
12
11.5 10.5 11.5 10.5 12.5 11.5
10.5 9,5
a:5 10.5 9.5
,
,
438.440 *39.2t.9* *41,0*7* 440.90?, 435.397* *35,252
445.132 443.3&5*
W5.24.) 441,221 44,.04?*
7
-3 3
:
3 -1 -2 -9 -2
:
-4 4
2
:
-3 4 -4
4
“3 0
-1 -4 0 -1 0
-4
-2 ..,
2 -6 2
0 -1
i
L
-i
15 ::
::
I2 12 13 13 13 13 14 14 !i
: 1
1 1
: ;
: 1 1 1 1
1
15 ::
14 15
:: 1;
11 11 13 13 12 12 1*
::*: 15:5
14:s 15,5
::*: ;;:;
12.5 11 5 13’5 12:s 13.5 12.5 14.5
iz;5 1’,5 13.5 14.5 13.5 15.5 1a.5 15.5 16.5 16.5 15.5
13.5 12.5
,
:za ::: 4856 l4*.m51 .4..??3 ..L.PI. .4..685 c12.211 w2.111 444.501 444.274 .39.21). .39.,99
l
::x:: 51:950 659.ao1 .4?.312
16.5?.9?9” .5?.9111 l5*.959, 459.595 .57*3&m .5?.919 455.701 .55..99” .56.559 456.205 454.517 .5..55m l55..91* 455.2409 k53.991 l52,9*a 45*.2.19 l53.995 .5l..OI9 l51.295 .52.7*5 , +52.509j I
:
l
31;9539 435.7.1 435.511 428.529 WO. 590 432,770 632.547 W..bPe., 624,515) 429.5m w9.3e.7 .2l.l86 .25.999 -4
0
0
:
;
-i -2
: 2
-4
: 0
:
: -3
1:
-:
: 10
-10
-:
-:
-1
-11 4
-I
: :
1: :
-2”
P
0
0
0 0
P 9
::
:0
: :
::
0 :
: 6
0 0
: :
t 5
12 12
:
:
: 0
: 0 0
: 2 2
:: ::
:
0 0
14
1, 13
12 12
:: 11 1,
9 9
: :
:
: :
:
: :
:
1r.5 19.5
1z.5 13.5
12.5 11.5
‘OS5 Y.5 11.5 10.5
Y:5 8.5
0.5 1’5 8.5 1’5
*#5 b’5 5’5
*‘5 3’5 5’5
:+:
0’5 1 5 2’5 1:5
0 5 0:5
KA’
::
16 lb
13 13
:: ::
10 10
: z
b :
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DYE LASER SPECTROSCOPY
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350
KAKIMOTO,
SAITO, AND HIROTA
ACKNOWLEDGMENTS The computer program used in the present work was written by K. Kawaguchi, whom the authors wish to thank. The authors are also grateful to J. T. Hougen for reading the manuscript. Numerical calculations were carried out at the Computer Center of the Institute for Molecular Science.
RECEIVED:
May 3, 1979 REFBRENCES
I. I. R. SLAGLE, R. E. GRAHAM, AND D. GUTMAN, Znr.J. Chem. Kinet. 8, 451-458 (1976). 2. U. SCHURATH,M. WEBER, AND K. H. BECKER,J. Chem. Phys. 67, 110-119 (1977). 3. S. GLAVAS AND S. TOBY, J. Phys. Chem. 79, 779-782 (1975). 4. A. B. SANNIGRAHI,K. H. THUNEMANN,S. D. PEYERIMHOFF, AND R. J. BUENKER,Chem. Phys. 20, 25-33 (1977). 5. H. E. RADFORD,K. M. EVENSON,AND C. J. HOWARD, J. Chem. Phys. 60, 3178-3183 (1974). 6. J. T. HOUGEN, H. E. RADFORD,K. M. EVENSON, AND C. J. HOWARD, J. Mol. Spectrosc. 56, 210-228 (1975). 7. J. W. C. JOHNS,A. R. W. MCKELLAR,AND M. RIGGIN,J. Chem. Phys. 68, 3957-3966 (1978). 8. A. R. W. MCKELLAR,J. Chem. Phys. 71, 81-88 (1979). 9. Y. BEERSAND C. J. HOWARD, J. Chem. Phys. 63,4212-4216 (1975). , 10. Y. BEERSAND C. J. HOWARD, J. Chem. Phys. 64, 1541-1543 (1976). II. S. SAITO, J. Mol. Spectrosc. 65, 229-238 (1977). 12. S. SAITO AND C. MATSUMURA,J. Mol. Spectrosc., in press. 13. P. A. FREEDMANAND W. J. JONES, J. Chem. Sot. Faraday II 72, 207-215 (1976). 24. S. GERSTENKORN AND P. Luc, “Atlas du Spectre d’Absorption de la MolCcule d’Iode,” Ed. du CNRS, Paris, 1978. 15. I. C. BOWATER, J. M. BROWN, AND A. CARRINGTON, Proc. Roy. Sot. Ser. A 333,265-288 (1973). 16. N. OHASHI, M. KAKIMOTO,S. SAITO, AND E. HIROTA,J. Mol. Spectrosc., in press. 17. R. F. CURL, J. Chem. Phys. 37, 779-784 (1962). 18. C. E. MooRE,.“A~~~~~ Energy Levels,” NBS, Washington, D. C., 1949. 19. I. R. SLAGLE, F. BAIOCCHI,AND D. GUTMAN, J. Phys. Chem. 82, 1333-1336 (1978).
OF
MOLECULAR
SPECTROSCOPY
Doppler-Limited
(1980)
80,334-350
Dye Laser Excitation the HSO Radical
Spectroscopy
of
MASAO KAKIMOTO, SHUJI SAITO, AND EIZI HIROTA Institute for Molecular
Science,
Okazaki 444, Japan
The cw dye laser excitation spectrum of the A *A’(OO3)t d zA”(OOO)vihronic transition of the HSO radical was observed between 16 420 and 16 520 cm-r with Doppler-limited resolutjon, 0.03 cm-‘. The HSO radical was produced by reaction of discharged oxygen with H,S or CH,SH. The observed spectra were assigned to 751 transitions of the K: c K6;=2+3, 1+2,0+-l, 1+0,2+1,and3 + 2 subbands, and were analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation interaction constants with good precision. The signs of the spin-rotation interaction constants were determined for both the upper and the lower state from the observed spectra. The band origin obtained is 16 483.0252 (2.5~ = 0.0013) cm-r. The molecular constants which were determined reproduce the observed transitions with an average deviation of 0.0045 cm-l. INTRODUCTION
The HSO radical has been the subject of various discussions. From reaction kinetics studies (I -3), HSO is expected to play an important role in various oxidation reactions of hydrogen sulfide or mercaptans, whose mechanisms are not fully understood because of the complexity arising from the tendency of the sulfur atom to form hydrogen- and oxygen-containing intermediates of varying structure and composition. Slagle et al. (I), on the basis of a reaction kinetics study with crossed jets, suggested the formation of HSO in reactions of various mercaptans with atomic oxygen. Schurath et al. (2) observed chemiluminescence spectra emitted in the reaction system of H,S (or D2S), atomic oxygen, and OS, and concluded that the spectra they observed were due to HSO (or DSO) through vibrational analyses of both the HSO and the DSO spectra and through a molecular structure determination by means of band-contour simulation of one of the HSO bands. These experimental findings stimulated an ab initio calculation study (4) on this new radical to predict such properties as the geometry, the dipole moment, and the vibrational frequencies. The HSO radical is interesting also from a spectroscopic viewpoint because of its similarity in molecular structure of the HOz radical, which has been studied extensively by far-infrared (5, 6) and infrared (7,8) laser magnetic resonance, microwave absorption (9-12), and near-infrared emission (13) spectroscopy. No high-resolution spectroscopy on the HSO radical has, however, been reported in any frequency region, and nothing is known accurately about the geometry or the vibrational frequencies of this radical in the ground or in any excited electronic state. The present paper is concerned with the first high-resolution study of the HSO radical, and presents precise molecular constants for both the lowest excited and 0022-2852/80/040334-17$02.00/0 Copyright All rights
0 1980 by Academic of reproduction
Press.
in any form
Inc. reserved.
334
DYE LASER SPECTROSCOPY
OF HSO
335
FIG. 1. Block diagram of the laser excitation spectrometer. BSI through BS3 are Pyrex glass beam splitters, Ml through M3 are 100% reflection mirrors, F stands for optical filters (Hoya R62), L for a lens system, and PM1 and PM2 denote photomultipliers (HTV R666S). ET. 1 is a piezo-mounted confocal etalon of FSR 2 GHz, driven by a high-voltage saw tooth, and used as a spectrum analyzer. ET. 2 is a temperature-stabilized confocal etalon of FSR 1.5 GHz. PDl and PD2 are silicon photodiodes.
the ground electronic states, determined from a rotational analysis of a cw dye laser excitation spectrum in the visible region. The resolution of the present method is entirely limited by the Doppler width of the HSO radical, 0.9 GHz. EXPERIMENTAL
DETAILS
The experimental arrangement is shown schematically in Fig. 1. The fluorescence cell was made of a Pyrex glass tube 35 mm in outer diameter and 600 mm long, sealed with a Pyrex glass Brewster-angle window at each end. A few tens of watts, 2450-MHz microwave discharge cavity was placed about 40 cm upstream of the cell. The discharged products and the reactant were introduced into the cell through the inner and outer coaxial tubes of a side arm, were mixed right at the entrance to the cell, and were pumped out continuously from the cell by a mechanical booster pump followed by a rotary pump. The linear flow speed was estimated to be about 20 m/set at 100 mTorr. The dye laser beam, collimated to about 1.5 mm diameter, entered and left the cell through the Brewster-angle windows. A photomultiplier (HTV R666S) was placed about 5 cm downstream from the mixing point, and the fluorescence light was collected through the wall of the cell withf - ‘/2 optics (L in Fig. 1). The scattered light was reduced by light baffles inside the cell and was blocked by four sheets of Hoya R62 edge filters (cutting off h < 620 nm) in front of the photomultiplier. The laser beam was mechanically chopped at 1.65 kHz and the signal from the photomultiplier was detected by a lock-in amplifier (PAR 124A) operated at the same frequency.
336
KAKIMOTO,
SAITO, AND HIROTA
616'606
'51.1Le'~0,1L
n
132.12-13112
I
I
I
I
.8
16487.0
.2
.c
cm-’
FIG. 2. An
example of excitation spectra. The upper trace is the excitation spectrum of HSO A 2A’(O03) +- J? *A”(OOO)and the lower trace is the iodine excitation spectrum with frequency marker (1.5~GHz separation). Reaction pressures were 0, 18 mTorr and H,S 70 mTorr, and the laser power was about 80 mW.
A dye laser (Coherent Radiation Model 599) was pumped by 5 to 6 W output from an argon ion laser (Spectra Physics Model 171-05) in the all-line operating mode. The dye laser was operated in single mode with Rhodamine 6G as the lasing dye. The dye laser output power (measured after Ml in Fig. 1) varied from 80 to 40 mW, as the thin etalon in the laser cavity was tilted to tune the laser frequency. The dye laser linewidth was not directly measured, but was found to be less than the bandpass of the spectrum analyzer monitoring the laser mode, i.e., less than 6 MHz. This enabled us to observe Doppler-limited spectra in the visible region. In fact, the observed widths of the HSO lines agreed well with the calculated Doppler width, 0.9 GHz fwhm. A single scan of the dye laser covered about 29 GHz, and two successive scans were shifted by 10 GHz in frequency, so that each HSO line was observed at least twice, and usually three times. An g5-cm double monochromator (Spex 14018) was used to roughly locate the dye laser wavenumber. The precise wavenumber measurement was done in the following way (see Fig. 1). A part (-8%) of the dye laser output was diverted from the main beam going to the cell by a Pyrex glass beam splitter BSl, and was further divided into three parts by Pyrex glass beam splitters BS2 and BS3. The first part (from BS2) was used to monitor the dye laser mode by means of a spectrum analyzer ET. 1 (FSR 2 GHz). The second part (from BS3) went into a temperature-stabilized etalon ET. 2 (FSR 1.5 GHz), whose fringes were used as frequency markers. The last part of the dye laser beam passed through a glass cell filled with IZat the saturated vapor pressure. The excitation spectrum of IZ and the superimposed frequency markers coming from ET. 2 were recorded at the same time as the HSO excitation spectrum on a two-pen strip chart recorder. A typical example of the recorder trace
337
DYELASERSPECTROSCOPYOFHSO N=9
/
I
I
we70
16465
'
cm
-1
FIG. 3. A part of the HSO excitation
spectrum. Assignments are indicated only forPQ,,PRI, ‘Qn, and but most of the remaining lines are also assigned (see Table Al). The lower trace is excitation spectrum.
rRR, transitions, the iodine
is shown in Fig. 2. The wavenumbers of the I, lines have been measured precisely (with a precision of 10m3to lo4 cm-‘) by Gerstenkorn and Luc (14), and these were used as the standards to measure the wavenumbers of HSO lines. The maximum deviation among wavenumber determinations for a single line from several scans was about 0.003 cm-’ in most cases. To optimize radical generation we tuned the dye laser to about 16 480 cm-‘, which, according to Schurath et al. (2), corresponds to the peak of the A 2A’(O03)+= d 2A"(OOO) band of HSO, and we monitored the strength of the fluorescence signal for several chemical reactions. We found that the reactions
(02)disch + CHsSH
(1)
(Q)disch + H2S
(2)
and gave the same fluorescence excitation spectrum in this region with good S/N ratio. The best S/N ratio was obtained when the CH,SH or H,S pressure was high enough, as compared to that of 02, to quench the SO, chemiluminescence, but the total pressure was not too high. Typical partial pressures used were 18 and 22 mTorr, respectively, for 0, and CH,SH in reaction (1) and 10 and 40 mTorr, respectively, for 0, and H,S in reaction (2), although optimum conditions seemed to depend on the immediate past history of the cell, the pumping speed, and the distance between the mixing point and the observation point. Reaction (2) was used for subsequent observations. We initially concluded that the spectrum we observed was due to HSO because reactions (1) and (2) gave identical spectra, and the position of the spectrum agreed with that of Schurath et al. (2). This initial assumption was fully supported by all of the spectroscopic constants deduced from an analysis of the high-resolution spectrum. The spectral region studied extends from 16 420 to 16 520 cm-‘. The PSD time constant used was 1 set and the scan rate was about 1 GHzllS sec. ROTATIONAL
ANALYSIS
In this work we adopt the vibronic assignment of Schurath et al. (2). The observed spectrum thus corresponds to the A 2A‘(003) + J%2A"(OOO) vibronic band,
338
KAKIMOTO,
SAITO,
AND
HIROTA
and rovibronic transitions accordingly obey c-type selection rules. Figure 3 shows a part of the spectrum. As seen in the figure, two series of strong lines can easily be recognized, which we assigned to the Q branches of the K; t K’; = 1 t 0 and 0 t 1 subbands, respectively, since neither series shows K-type doubling. Another series of fairly strong lines, which is only barely seen in Fig. 3 but is more prominent in the higher-wavenumber region, was also picked out and was assigned to the R branch of the Kh t Kz = 1 t 0 subband. It was found that the K, assignment of Schurath et al. (2) should be shifted by one unit, i.e., their K; + Kg = I + 0, 2 + 1, 3 + 2 should be replaced by KL + Kg = 0 + 1, 1 -+ 0, 2 + 1. This reassignment is based on our observation of the K-type doubling for the Kh t K; = 2 + 1 subband. Spin splittings were observed in the rR,, transitions and in the low-N transitions of the rQOand PQ1 branches: the spin splitting of the Q branches becomes smaller as N increases and eventually the two components overlap each other within the Doppler width, as shown in Fig. 3. From the N assignment of these three branches alone, a fairly good set of rotational constants and spin-rotation interaction constants was obtained to start with, except that the ground-state A value was fixed to that calculated from the molecular structure of Schurath et al. (2). The assigned lines were analyzed by the method of least squares and the parameters thus obtained were in turn used to assign other lines with higher N and/or K, values. This cycle of least-squares fit and assignment of lines was repeated; the number of adjustable parameters was increased gradually as more lines were assigned. The signs of the spin-rotation interaction constants, the E,,‘s, were determined in the following way. Among the four possible sign combinations, (e&,&J = (+,+), (-,-), (+,-), and{-,+), the first twocombinations, (+,+) and (-,-), were easily eliminated by using the observed line frequencies of four branches, PQI,TQ,,, rR,,, and ‘Q1. In order to discriminate between the two remaining cases, (e&&J = (+ , -) and (- , +), it was necessary to observe the rather weak transitions with N 5 3. The case of 'R,,(O) is shown in Fig. 4 as an example. As seen in a
I
I
I I I
I
.a
I 16L93.0
I I I
I
I
.2
.L
I
.6 cm-’
FIG. 4. The excitation spectrum of HSO around l,, c O,O. Vertical lines indicate the calculated spectra. Stronger lines areJ’ cJ” = S/Zt 1%and weaker IinesJ’ +-J” = 44 + %. Solid lines corre) = (-,+). (The assignment of other lines is a: spond to (&,E:.) = (+,-) and broken lines to (EL, C” (111 llL10 + 100,10, b: 173.14 + 172,,6, c: 123.,0 + 132,12r and d: 11~ +- 11~~0.)
DYE LASER SPECTROSCOPY
OF HSO
339
the figure, only the (e&e&) = (+ ,-) sign combination reproduces the observed spectral pattern in both the line position and the relative intensity. Thus we have determined experimentally that E,, is positive in the A *A ’ state and is negative in the x 2A” state. The following Hamiltonian was used in the analysis: H = Hot + & H,,, = AN;
(3)
+ I-L
+ BN; + CNf,
(4)
Hcd = -AN(N2)* - ANKNIN: - AKN; - 2S,N’(N”, - Nf)
- &{(N; H,, = l,,N,S,
+
EbbNbSb
+
- N2,)N2, + N2,(N; - Nf)},
(5) (6)
G,NJ,
for both the upper and the lower states, where the notation follows that of Bowater et ai. (15). It was found to be unnecessary to include higher-order terms in the centrifugal distortion Hamiltonian, I&,. The effect of centrifugal distortion terms in the spin-rotation interaction was examined, but these did not improve the fit at all. The energy matrix was set up with Wang-type symmetric-top wavefunctions as bases, where all matrix elements of the type AJ = 0, AN = 0, -+l, and AK, = 0, k2 were included, and was diagonalized to give the energy eigenvalues. In this way, 646 of 781 observed lines were assigned to 751 transitions. The subbands studied are summarized in Table I and all the assigned transitions are listed in Table Al of the Appendix. Most of the observed lines which remain unassigned are higher- or lower-N transitions of the subbands listed in Table I or high-N TABLE 1 Studied Subbands of HSO A ‘A ‘(003) 6 $? *A”(OOO)
Ka’ + Ka" 2
+
3
1+2
0
-1
1+
0
transitions
a
(Ib
P(3) Q(3) R(8)
-
P(6) Q(l0) R(15)
16 23 29
P(2) Q(2) R(7)
-
P(12) Q(16) R(22)
34 48 51
P(1) Q(l) R(1)
-
P(15) Q(21) R(24)
29 40 46
P(Z) Q(1) R(O)
-
P(20) Q(23) R(25)
35 44 51
P(7) Q(3) R(3)
-
P(21) Q(24) R(22)
49 81 74
P(12) Q(9) R(15)
-
P(18) Q(23) R(21)
21 57 23
2
-1
3
f
a
Minimum and maximum N values are indicated in parentheses.
b
Number of transitions used in the least-squares fit.
2
340
KAKIMOTO,
SAITO, AND HIROTA
transitions of the KA + Kz = 4 + 3 subband. These lines were, however, not included in the analysis since they were usually too weak or too heavily overlapped. Even among those assigned lines listed in Table I or Table Al, it often happened that more than one transition had to be assigned to the same observed line. When the overlapping resulted in shoulders or broadening of lines and thus made wavenumber measurement inaccurate or even impossible, these lines were not included in the least-squares fit. In Table Al the calculated wavenumbers, rather than the observed wavenumbers, are listed for these transitions in parentheses. On the other hand, in the case of exact coincidence of two or more transitions within the Doppler width, which did not cause any apparent shoulder or broadening, these blended lines were included in the least-squares analysis. All the lines used in the least-squares fit were given the same weight, irrespective of their intensity or multiple assignment. The molecular constants determined for the excited and the ground states are listed in Table II. The rms deviation between the observed and the calculated wavenumbers is 0.0045 cm-‘, which is only slightly larger than one-tenth of the Doppler width, 0.9 GHz or 0.03 cm-‘. No evidence of perturbation in the excited state was observed. DISCUSSION
Dye laser excitation spectroscopy, which was utilized in the present work, enables us to achieve very high sensitivity and very high resolution. The resolution is entirely Doppler limited and is nearly 10 times better than that of conventional high-resolution spectroscopy. As a result we were able to determine the molecular constants of the HSO radical in both the A *A'(OO3) and the J? *A"(OOO) states with high precision. The band origin we obtained, 16 483.0252 (13) cm-*, TABLE II Molecular Constants of HSO (MHz)
constant
; *A"(OOO)
A %'(003) 291 862(16)
A
299 478(20)
B
16 934.7(17)
20 504.4(17)
C
15 802.1(17)
19 135.6(17) 0.0318(25)
0.0483(22)
0.857(58)
3.318(38)
27.2(20)
39.9(18)
E
0.00506(58)
0.00202(56)
4.01(41)
0.45(38)
17 854(165)
aa
Ebb E cc
-433(32)
-352(32)
-5(32)
VO a
in cm
Numbers standard digits.
-1
-10 292(64)
87(32)
= 16 483.0252U31a
.
in parentheses deviation
are 2.5 times
and apply
the
to the last
DYELASERSPECTROSCOPYOFHSO
341
is 21 cm-’ higher than that of Schurath et al. (2), 16 462 cm-‘. This difference is entirely due to their improper assignment of the K, values. In a subsequent paper (16), the present results will be combined with those for DSO, for which excitation spectra are now being analyzed, to provide more information on the molecular structure and force field. The sign of the ground-state spin-rotation interaction constant, E:,, can be estimated from the theoretical expression (17), I, 2 I(OIL&z) I’/(& - E,,). (7) %l = -4A.ASo 11
If, as a first approximation, we assume that (a) only the A 2A’ state makes a dominant contribution to the sum in Eq. (7), (b) I (2 IL, IA > I 2 is unity, and (c) the spin-orbit coupling constant As0 is equal to that obtained from the ground-state spin splitting of the neutral sulfur atom, As0 = - 177 cm-’ (18), then e& is calculated to be -0.43 cm-’ or -13 GHz. This calculation supports the sign of &, determined in the present work. A negative E:, is also supported by the extremely well determined (I 1) negative value of &, for the HO, radical, whose electron configuration is similar to that of HSO. As already mentioned, Schurath et al. (2) used the following reaction system to observe the chemiluminescence of the HSO radical: H2S + (02)disch + 0,.
(8)
Their thermochemical argument suggests that ozone is required for the production of the HSO radical, especially in its electronically excited states. The reaction mechanism they proposed is the well-established initial oxidation of H,S: H,S + 0 + SH + OH
(9)
SH + 0, + HSO* + 0,.
(10)
followed by We, on the other hand, did not use ozone because we wished to avoid strong chemiluminescence, but we were still able to observe the HSO spectrum with the reaction (2). This means that the reaction route, H,S + 0 -+ HSO + H,
(11)
might be responsible for the production of HSO. But the question then arises why reaction (1 l), which seems to be endothermic, can compete with an exothermic route, reaction (9). One possibility is, as Slagle et al. (29) mentioned, that reaction (11) might be slightly exothermic. Another possibility is the presence of a small amount of 0, formed by microwave discharge in 02, which allows route (10) to take place, although the production of O3 from atomic oxygen and molecular oxygen requires a third body, that is, high pressure. The information established in the present paper should be useful in kinetics studies spectroscopically monitoring the concentration of HSO as an intermediate. APPENDIX
Table Al lists the observed transitions of HSO A 2A’(O03) +- 2 “A”(OO0). Wavenumbers in parentheses are calculated values. An asterisk indicates a line assigned more than once. 0 - C stands for 1O+3times the observed wavenumber minus the calculated wavenumber.
P2
:
:
: 2
3 :
:
:
:
: 2
2 2
: 2 2
:
:
:
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: 3
:
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3 3
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LWEP
:
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:
5 5 :
. :
a
:
II
TABLE Al
04-1
1.221) ,..22 1.575
8;787
‘~052~ ,908. ‘~8521 .9Cd* .409*
16437.70, 437.008 437.L61 437.Ob4 *,6.70,* 436.165
16.3
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14 I5
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10 10
N
:
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2
3
: 5 -1 -6 3 -2
:
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:
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List of Transitions of HSO A *A’(OO3)t_??
15
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:s 5.5 6.5 5.5 715
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::: 4.5 3’5 4.5 315 5.5
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::*: 11:5
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10:5 11.5 10.5 12.5
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0.5 8.5 10.5 ,z
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412,217. 431,925) 431.71)b 430. .74 630.058 l30.27, .29.869 .~~ 428.150,
.3,.92,, 5,,.564 43,..55 432.362
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426.789 426.911
431,825 431*,12*
:::*:;: 43&3b7
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455.898 *55.796 452.521 +52,422* *w.ow 448.793
459.019 *t.1,7,5 458.916”
w.4.593 464.383 461,876
wl6.73P 466.856
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Al-Continued
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1,607. 1.233” 1.233” .6351 ,635ll
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lb.7
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-7 -11 0 6 -6 15 -1
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: -1
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: 3
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7 -1 5 0
O-C
w %
DYE LASER SPECTROSCOPY
OF HSO
345
1* 16 15 15 lb 16 17 17 18
22 22 2,
0
.i
0 0 0 0 0
0 0 0
::
::
18
:: 17 18
:: 2,
22.5 21.5 2,.5
14.5 13.5 15.5 16.5 1615 15.5 17.5 16.5 18.5
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3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
12 I2 :: 13 13 13 14 L4 :: 15 15 15 15 16 16 :: 17 17 1, 17
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:
9 9 8 10 8
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P 11 11 11 ::
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10 P 11 P
22 ::
2 :
23 23 23
-; -3 2
21 :: 2Ll
4
2 ; 2
N L* KC
Al-Continued
22 22 22
-4 -3
O-C
TABLE
11.5 10.5 11.5 10.5 12.5 11.5 12.5 11.5 13.5 12.5 13.5 12.5 14.5 13.5 14.5 13.5 15.5 14.5 15.5 14.5 16.5 15.5 lb.5 15.5 17.5 lb.5 17.5 lb.5
23.5 12.5 ::::
21:5
22.5 ;:;;
,
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7 z 2 2 2 2 7 2 :
: 2 2 2 2 : 2 2
z
: : 2 : 2 * : 2 z
:t 14 :: 15 15 15 15 lb lb :: 1, 1, 1, 1, :: 1s 18
:
: :: 10 :: :: 11 :: ::
*7
12 11
z *
10 9
R 10 R
: :
B 8
Ib lb
I* 16 lb lb 15 15 ::
12 14 14 13 13 ::
11 13 13
11 10 :;
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21 21 20 2”
2 7 7 :
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1 1 1 1
:: 12 12 13 13 13
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2, ::
12.5 11.5 11.5 12.5
10.5
11.5 10.5
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fl:5 t*: lO.5 9.5
9.5
18:5 17.5
lb:5 15.5 17.5 16.5 17.5 lb.5 :t.:
13.5 1*.5 15.5 19.5 15.5 lb.5 :2:
14.5 12.5 13.5
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21.5 20.5 21.5 al.5
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5LO.eI5 510.005 510.325 3OP.03W
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488.231 480.6e.3, l8*.*11 483.991, *a*.027 W33.60** 474.623 479.217
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6
0
3 -2 b 3
-:
-:
: 10 0
-:
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1;
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4 : ::
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-:
-11
5 -7 4 13 2
7 .
3 :
:
5
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:
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Y W
350
KAKIMOTO,
SAITO, AND HIROTA
ACKNOWLEDGMENTS The computer program used in the present work was written by K. Kawaguchi, whom the authors wish to thank. The authors are also grateful to J. T. Hougen for reading the manuscript. Numerical calculations were carried out at the Computer Center of the Institute for Molecular Science.
RECEIVED:
May 3, 1979 REFBRENCES
I. I. R. SLAGLE, R. E. GRAHAM, AND D. GUTMAN, Znr.J. Chem. Kinet. 8, 451-458 (1976). 2. U. SCHURATH,M. WEBER, AND K. H. BECKER,J. Chem. Phys. 67, 110-119 (1977). 3. S. GLAVAS AND S. TOBY, J. Phys. Chem. 79, 779-782 (1975). 4. A. B. SANNIGRAHI,K. H. THUNEMANN,S. D. PEYERIMHOFF, AND R. J. BUENKER,Chem. Phys. 20, 25-33 (1977). 5. H. E. RADFORD,K. M. EVENSON,AND C. J. HOWARD, J. Chem. Phys. 60, 3178-3183 (1974). 6. J. T. HOUGEN, H. E. RADFORD,K. M. EVENSON, AND C. J. HOWARD, J. Mol. Spectrosc. 56, 210-228 (1975). 7. J. W. C. JOHNS,A. R. W. MCKELLAR,AND M. RIGGIN,J. Chem. Phys. 68, 3957-3966 (1978). 8. A. R. W. MCKELLAR,J. Chem. Phys. 71, 81-88 (1979). 9. Y. BEERSAND C. J. HOWARD, J. Chem. Phys. 63,4212-4216 (1975). , 10. Y. BEERSAND C. J. HOWARD, J. Chem. Phys. 64, 1541-1543 (1976). II. S. SAITO, J. Mol. Spectrosc. 65, 229-238 (1977). 12. S. SAITO AND C. MATSUMURA,J. Mol. Spectrosc., in press. 13. P. A. FREEDMANAND W. J. JONES, J. Chem. Sot. Faraday II 72, 207-215 (1976). 24. S. GERSTENKORN AND P. Luc, “Atlas du Spectre d’Absorption de la MolCcule d’Iode,” Ed. du CNRS, Paris, 1978. 15. I. C. BOWATER, J. M. BROWN, AND A. CARRINGTON, Proc. Roy. Sot. Ser. A 333,265-288 (1973). 16. N. OHASHI, M. KAKIMOTO,S. SAITO, AND E. HIROTA,J. Mol. Spectrosc., in press. 17. R. F. CURL, J. Chem. Phys. 37, 779-784 (1962). 18. C. E. MooRE,.“A~~~~~ Energy Levels,” NBS, Washington, D. C., 1949. 19. I. R. SLAGLE, F. BAIOCCHI,AND D. GUTMAN, J. Phys. Chem. 82, 1333-1336 (1978).