The infrared spectrum of GeO

JOURNALOF MOLECULAR SPECTROSCOPY 116, 136- 142 ( 1986)

The Infrared Spectrum of GeO G.

A.

THOMPSON,

A. G. MAKI, AND A. WEBER

MolecularSpectroscopyDivision,NationalBureau of Standards. Gaithersburg,Maryland 20899 The high-temperature infrared spectrum of the Av = 1 sequence of GeO has been investigated from 882 to 955 cm-’ with a tunable diode laser spectrometer. Transitions from “Ge160, ‘*Ge160, 73Ge’b, “Ge160, and 76Ge’60 were measured for vibrational transitions from u = 1-O to u = 6-5 and fit to a single set of eight Dunham potential coefficients. 0 1986Academic RSS, I~C. INTRODUCTION

The ultraviolet spectrum of GeO contains several bands which have been the subject of high-resolution absorption (Z-3), and emission (4, 5) spectroscopy. These studies provide a fairly complete understanding of the rotational and vibrational structure of several low-lying electronic states. The infrared spectrum of GeO isolated in nitrogen and argon matrices has also been studied (6, 7). Microwave measurements have been made on the J = 1-O transitions of the five stable germanium isotopic species of GeO in the ground vibrational state as well as in some higher vibrational states (up to u = 2) (8, 9). The magnetic properties and electric dipole moment have also been investigated (9-22). Despite the considerable interest in this molecule, the higher order spectroscopic constants which describe the potential energy curve for the ground electronic state (X’Z) were not determined prior to this work. In this paper we report the 8 Dunham coefficients describing the ground state potential function and 17 Dunham Yij rovibrational constants calculated from the potential constants. These constants were obtained by fitting over 100 Av = 1 transitions in GeO with an uncertainty of 17 MHz (5.5 X 10m4cm-‘). EXPERIMENTAL

DETAILS

Gas phase GeO was formed by heating an equimolar mixture of GeOZ and elemental germanium to about 750°C under vacuum. As the first intense spectra were observed a buffer gas of 5-8 Torr of Argon was introduced into the cell to minimize the migration of material out of the hot zone of the sample cell. An initial charge of 12 g of the GeOz/Ge mixture was sufficient to permit taking measurements for at least 6 hr. The stainless-steel sample cell was approximately 80 cm long and 28 mm in diameter. The central portion of the cell was heated in a resistively heated tube furnace which maintained a fairly uniform temperature across approximately 40 cm of the tube. The ends of the absorption cell were outside the furnace and the NaCl windows were at room temperature. Temperatures were determined with a chromel-alumel thermocouple. 0022-2852186 $3.00 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form resewed.

136

INFRARED SPECTRUM OF GeO

137

The infrared tunable diode laser spectrometer used in these experiments has been described previously (13). The two diodes used in these experiments gave tunable laser radiation over several regions between 882 and 955 cm-‘. Measurements were calibrated with either OCS or NzO, depending on the particular frequency range being measured. The OCS atlas used was calculated from constants based on very accurate heterodyne measurements against the 13C02 laser (14, 15). This calibration atlas spans the region from 800 to 893 cm-’ and is judged to be accurate to within +2 MHz for the calibration lines that were used. The calibration for frequencies greater than 900 cm-’ was based on N20 absorption lines that correspond to the laser transitions of the lO”O-00” 1 band. The N20 frequencies were calculated from constants taken from Ref. (16) which were based on very accurate heterodyne measurements of the N20 laser transitions (17), less accurate heterodyne measurements of the absorption lines of the 00” l-OO”0 band, and on other infrared and microwave measurements as outlined in Ref. (16). The N20 calibration frequencies are accurate to f 1 MHz. The N20 calibration gas was at a pressure of 4 Torr in a 45-cm-long absorption cell which was heated to about 80°C. Procedures used to minimize systematic errors are described in Ref. (18). The major source of uncertainty in these measurements is believed to arise from the determination of the difference in frequency between the GeO lines and the calibration features. The uncertainties listed in Table I represent an estimate based on the proximity to a calibration line and the signal to noise ratio of the measured line. ASSIGNMENT AND ANALYSIS OF THE MEASUREMENTS

A portion of the observed spectrum is shown in Fig. 1. The five naturally occurring isotopes of germanium were observed in Au = 1 transitions from the six lowest vibrational states. The spectra were analyzed by relying on existing rotational (8, 9) and vibrational (I) data to calculate the anticipated spectrum for each major isotope. Although the existing data did not permit the accurate determination of line positions, the predicted frequency differences between rotational transitions within a given vibrational sub-band were used to assign the most intense transitions observed. The relative intensities were an important guide in making the assignments. The assigned transitions were then included in the calculation of a more realistic spectrum which was then used to assign the rest of the diode laser spectrum. Only a few weak lines could not be assigned and were assumed to be due to impurities. No lines due to other isotopic species (such as 74Ge180) were observed. The observed lines listed in Table I were fit to a set of Dunham potential constants by an iterative nonlinear least-squares calculation using an improved version of the computer program used in Refs. (19, 20). Also included in the least-squares fit, but not given in Table I, are the pure rotational transitions, measured by microwave techniques, taken from the literature (8, 9). The unsplit J = 1-O rotational transition frequency for 73Ge0 was calculated from the quadrupole split transitions and constants given in Ref. (8). The Dunham potential constants given by the fit are given in Table II. Table III gives the Dunham Yijro-vibrational constants calculated from the potential constants in Table II for the three most abundant isotopic species. To relate the potential constants

138

THOMPSON,

MAKI, AND WEBER TABLE I

Observed Wavenumbers of Germanium Oxide Transitions Y’ - V” Rot. Trans.

Wavenumber

UNC

(cm-')

o-c

Y' - V"

Rot. Trans.

(cm-')

Wavenumber

UNC

(cm-‘)

o-c

(cm-‘)

%O

1

956.39441(50) 954.69900(117) 911.20658(100)

-0.00005 0.00015 -0.00043 0.00016 -0.00088 -0.00024 -0.00042 0.00075 -0.00022 -0.00057 0.00061 -0.00032 0.00024 -0.00197 -0.00026 0.00058 0.00031 0.00048 0.00028 -0.00032 -0.00049

P(47)

907.82234(67) 956.30681(82) 911.32266(82) 910.25322(100) 882.84843(67)

0.00006 -0.00033 -0.00015 -0.00004 0.00010

0 0 0 0

P(22) P(24) P(27) ~(60)

957.13999(50) 954.92135(67) 951.54755(82) 9~1.00717(117)

0 1 1 1 1 1 1 1 2 2 2 2 2 2

P(80) P(l4) P(l6) P(19) P(51) P(53) P(54) P(74) P( 5) PC 6) ~(46) P(47) P(49) P(68)

883.37956(671 956.92190(67) 954.81134(50) 951.59936(67) 914.05919(82) 911.51726(100)

0.00006 0.00052 -0.00020 -0.00082 0.00004 -0.00015 0.00011

R( 3) P(40) P(42) P(62) R(13) X(11) R(23) P(27)

956.97000(67) 910.33171(100) 907.94109(100) 882.78929(67) 956.97598(117) 955.24858(82) 956.25248(67) 907.95239(100)

0 1 1 1 1 1 1 2 2 2 2 i i 4 4 4 5 5 5 65 6 6 6

72GeO 1 1 1 1 1 2 2 2 2 2 2 2 z 3 ; 3 4 4 4 4

0

P(20)

0 0

P(22) P(25) P(56)

0 0 0 1 1 1 1 2 2 2

P(56) P(59) P(79) P(l2) P(l4) P(l7) P(52) P( 3) P( 5) P(45)

2 z 3 4 4

P(67) R( 5) R( 3) P(38) R(l5) R(l3)

4 4 5 5 5

P(30) P(33) R(261 P(22) P(23)

5

3 3

5

11

z 6

5 5

4

957.04759(50) 954.86388(67) 951.543’5(82) 914.19391(50) 911.59702(67) 910.29145(82) 883.02548(67) 956.72147(100) 952.64440(67) 951.48501(100) 910.74776(100) 956.91093(100) 954.95665167) 910.86438(200) 882.72161(50) 956.52393(100) 954.69170(117) 910.64692(67)

910.23798(82) 883.49624(67) 957.23759(82) 956.24510(50) 911.68821(82) 910.45536(50) 907.97181(100) 883.26682(50)

-0.00059 0.00046 -0.00014 -0.00035 0.00011 0.00095 -0.00006 -0.00032 0.00000 -0.00022 0.00011 -0.00013 -0.00002 0.00022 -0.00032 -0.00022 0.0003? -0.00063 0.00019

6 7OGeO 1 10 10 10 10 10 10 2 2

5

~(48)

883.54254(67)

0

P(24) P(25) P(26) P(29) P(62) P(64) P(82) P(21) P(55) P(76) PC 8) P(10) P(l3) p(48) P(70) P(41) P(63) R( 8) P(57)

957.30811(100) 956.18229(50)

P(21) P(23) P(26) P(59) P(80)

957.08268(50) 954.88159(100)

1 1

:

: 2

;

2 2

i 4 4

2

5 5 73Ge0 1 10 10 10 10 2 2 2 2 2 3 ; 4 4 76&O 1 10 10 10 2 2 2 z 3 3 4 4 5

33 4 4 0

1 1 1 1 1 2 2 : 3 0

1 1 1 2 2 2 2 ; 4

P(l3) P(l5) P(50) P(55) P(74) P( 6) P(43) ~(46) P(38) ~(61) P(l8) P(20) PC571 P(78) P(10) P(12) P(50) P( 6) P(43) P(46) P(65) P(36) P(59) P(29)

955.05295(82) 951.62391(67) 910.47364(50) 907.78191(67) 882.56426(50) 951.78845(50) 911.08329(100) 882.66667(50) 956.63174(117) 954.59423(82) 951.49295(132) 911.35431(82) 882.52320(67) 911.28156(67) 883.45618(67) 954.98660(117) 882.77297(67)

951.53498(166) 911.29417(67) 882.52891(67) 956.80899(100) 954.71645(50) 914.27687(67) 907.92744(100) 882.54202(67) 955.09104(117) 914.30789(100) 910.65266(100) 911.65729(82) 883.13619(100) 957.02307(50) 954.87379(100) 910.94837(166) 882.64168(32) 956.58894(82) 954.54583(100) 911.30698(67) 951.80817(67) 911.32983(50) 907.70312(50) 883.57496(50) 911.01445(149) 882.97308(67) 910.36016(82)

0.00070 0.00123 0.00004 0.00127 -0.00036 -0.00014 0.00048 0.00015 0.00032 -0.00071 -0.00002 0.00104 -0.00008 -0.00090 0.00006 0.00144 -0.00014 -0.00093 -0.00006 0.00017 0.00006 0.00036 0.00017 -0.00013 0.00030 -0.00106 -0.00027 -0.00011 0.00010 0.00053 0.00046 0.00060 0.00078 -0.00056 -0.00082 -0.00026 0.00003 -0.00164 0.00002 0.00034 -0.00059 -0.00056 0.00055 -0.00042 -0.00016 0.00032 -0.00088 -0.00043 0.00025

to the ro-vibrational constants and energy levels the least-squares fitting program used the equations given by Dunham (21) and extended by Bouanich (22) and Ogilvie and Bouanich (23). The ui constants are assumed to be isotopic-ally invariant, and the values of Be and w, may be expressed in terms of the reduced mass (h) of the molecule and the isotopically invariant terms U, and U, by B, = UBp-’

(1)

139

INFRARED SPECTRUM OF GeO 76

T 74 73 74

T i

72

76

P,(59) . I

P,(50)

I

I

910.90

911.00

911.20

WAVENUMBER

911.40

(cm-l)

FIG. I. A portion of the infrared spectrum of GeO at 750°C. The isotopic species is noted above each transition. The vibrational and rotational assignments are noted below each transition. The lower vibrational state is indicated by a subscript on the rotational assignment. The line marked by an open circle is an impurity.

w, =

u,p.

The atomic masses used to calculate the molecular reduced masses in Table IV were taken from Ref. (24). Table II gives the potential constants through &. Attempts to fit with a7 as a variable gave values of a7 that were very large. Since the uncertainty in a7 was larger than its

TABLE II Dunham Potential Constant9 for GeO u, (MHz.u”‘l >c$PGEitkJ

cm-l

Be(74Ge160) e a1 a2

cm-’

:; a5 a6 Pm

I.R.

107243692.(44Jb 191469.9452(339) 986.49381(41) 0.485698240(86) -3.1457227(566) 6.2340001427) -9.72618(1018) 12.6995(1174) -13.646(494) 9.86(511)

dW.

Of

meas”rementS

0.00055

a) U, and Ub are defined in eqs. l-2. constants are dimensionless. b) The uncertainty in the last digits WrOr) is given in parentheses.

cm-’ The ai (one standard

140

THOMPSON,

MAKI, AND WEBER TABLE III

The Dunham Ro-Vibrational Constants” for GeO constant Y,o 50 YpJ Yqo

Tke’60

(cm-‘) (cm-’1 (cm-‘) (cm-‘)

99’.49566(42)

-4.469977(249)

-4.492079(250)

-4.515429(251)

0.0045983(551)

0.0046325(555)

0.0046686(560)

-0.00000625(403)

-0.00000631(407)

-0.00000638(411)

14632.8569(27)

14560.8617(27)

14708.9191(27)

-92.98171(254)

-92.29633(252)

(MHZ)

70ce’60

988.92875(42)

YO’ (MHZ) Y”

7*ce’60

986.49294(42)”

-93.70763(256)

Y2, (kHz)

40.16(122)

40.56(123)

40.98(124)

Y31 CkHz)

-0.293(148)

-0.296(150)

-0.300(152)

Yo2 ikHz)

-14.11863431130)

-14.25859691132)

-14.4072160(133)

Y,2 (Hz)

-16.320(27)

-16.523(27)

-16.738(28)

Y22 (Hz)

-0.2480(161)

-0.2517(164)

-0.2556(166)

Yg3 (mHz)

-1.99496(83)

-2.02470(84)

-2.05644(86)

y13 (PHz)

-87.10(144)

-88.61(147)

-90.24(149)

Y23 (PHz)

-1.277(367)

-1.302(374)

-1.329(382)

Yo4 (IIHZ)

-9.5510(40)

-9.7413(41)

-9.9455(42)

y14 CnHz)

-0.3092(111)

-0.3161(114)

-0.3236(116)

Y,J~(PHz)

-0.019395(136)

-0.019880(139)

-0.020402(143)

a) To convert b)

from cm-' to MHz multiply by 29979.2458. The uncertainty in the last digits (one estimated standard is given fn parentheses.

error)

value, we have felt justified in leaving out a7 and higher terms (which was equivalent to setting them equal to zero). The a6 term was included in the fit because its value was close to that of a5 (but with opposite sign) and it was expected that that was more realistic than setting it equal to zero (by leaving it out of the fit). Even though the Y, and Y3, terms are not determined to within three times their uncertainty, we give their values in Table III and they should be used in the application of Table III since they are correlated to the values of the other constants. In Tables II and III the constants are given with more digits than seems necessary when the uncertainties are taken into account. This is to allow for the correlation among the constants which requires that more significant figures must be retained in order to correctly calculate the observed transitions.

TABLE IV Reduced Mass and Natural Abundance of Germanium Isotopes Molecule

Reduced

74ce’60 76ce’ 60 73Ge’60 72&l 6o

13.14962538 13.21154275 13.11769962

7Oce’60

13.08492783 13.01726354

a)

Reference

24.

Massa

Natural

Abundance

7.8% 36.7% 7.8% 27.4% 20.5%

INFRARED

SPECTRUM

OF GeO

141

DISCUSSION

Our observed gas phase value for v0(74Ge0) = 977.5679 cm-’ is close to the argon matrix value of 975.3 cm-’ observed by Ogden and Ricks (6). Our values for Y10= 986.49294(42) cm-’ x o, and Y,, = -4.46998(25) cm-’ = -0,x, are in good agreement with the values of w, = 986.69(3) and W,X, = -4.50(4) given by Lagerqvist and Renhom (I) for 74Ge0. The values of Y,, , Y, , , and Yz, are in agreement with those given by Honejiiger and Tischer (9). The presently determined centrifugal distortion terms are much more accurate than the previously determined values given by Zymicki (4). One of the objectives of this work was to determine if there is any deviation from Eqs. (1) and (2) which might be attributed to a breakdown in the Born-Oppenheimer approximation. We now have quite good measurements on a number of transitions for the isotopic species “GeO, 72Ge0, 73Ge0, 74Ge0, and 76Ge0 and such a breakdown is not apparent in the deviations shown in Table I. To further quantify this point the data for GeO were also fit to a potential function similar to that used to fit LiF (20). This function replaces Eqs. ( 1) and (2) by Be=

&[l +g]/p

(3)

and (4) where A4, is the electron mass [5.4858026 X 10-4~.(25)] and Moe is the mass of the germanium atom. Equations (3) and (4) were used because they have the same form as suggested by Watson (26) for Yo, and Y,, (or Beand w,) which are the most accurately determined of the constants. Fitting the data with both A? and AC, B , or with A? alone, gave a value for A? that was about the same size as its uncertainty (A,Ge = 0.36 + 0.22). Since Ap is only about twice its uncertainty (AT = -3.2 + 1.5), it also is not significant. This was also affirmed by the standard deviation of the fit which, at most, was improved by 3% when either or both terms were added to the fit. RECEIVED:

September 3, 1985 REFERENCES

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

A. LAGERQVIST AND I. RENHORN,Physica Scripta 2S,24 I-256 ( 1982). 0. APPELBLAD,S. FREDIN,AND A. LAGERQVIST,Physica Scripta t&933-938 (1982). 0. APPELBLAD,S. FREDIN,AND A. LAGERQVIST,Physica Scripta 28, 160-170 (1983). W. ZYRNICKI,J. Mol. Spectrosc. 89, 557-560 (1981). P. D. KORZH AND M. I. KUZNETSOVA,O_ot. Spektrosk. 31, 539-541 (1971): Opt. Spectrosc. 31, 286288 (1971). J. S. OGDEN AND M. J. RICKS,J. Chem. Phys. 52, 352-357 (1970). A. Bos, J. S. OGDEN, AND L. ORGEE,J. Phys. Chem. 78, 1763-1769 (1974). T. TARRING,Z. Naturforsch. Zla, 287-289 (1966). R. HONERJAGER AND R. TISCHER,Z. Naturjbrsch. Da, 1374-1375 (1973). J. HOER, F. J. LOVAS,E. TIEMANN, R. TISCHER.AND T. TARRING, Z. Naturforsch. 244 12 17-122 1 ;‘ (1969).

142

THOMPSON,

MAKI, AND WEBER

II. R. E. DAVISAND J. S. MUENTER,J. Chem. Phys. 61,2940-2945 (1974). 12. J. W. RAYMONDA,J. S. MUENTER,AND W. A. KLEMPERER, 1. Chem. Phys. 52,3458-346 1 (1970). 13. T. R. TODDAND W. R. OLSON,.I. Mol. Spectrosc. 74, 190-202 (1979). 14. J. S. WELLS,F. R. PETERSEN, A. G. MAKI,AND D. J. SUKLE,Appl. Opt. 20, 1676-1684,2874 (1981). IS. J. S. WELLS,F. R. PETERSEN, A. G. MAKI, AND D. J. SUKLE,J. Mol. Spectrosc.89,42 l-429 (198 I). 16. J. S. WELLS,A. HINZ, AND A. G. MAKI, J. Mol. Spectrosc., in press. 17. B. G. WHITFORD,K. J. SIEMSEN,H. D. Bccrus, ANDG. R. HANES,Opt. Commun. 14,70-74 (1975). 18. A. G. MAKI, F. J. LOVAS,AND W. B. ORSON,J. Mol. Spectrosc.92,410-418 (1982). 19. A. G. MAKI AND F. J. LOVAS,J. Mol. Spectrosc.95, 80-9 1 (I 982). 20. A. G. MAKI, J. Mol. Spectrosc. 102,361-367 (1983). 21. J. L. DUNHAM,Phys. Rev. 41,721-731 (1932). 22. J. P. BOUANICH,.I. Quant. Spectrosc.Radiat. Transfer 19, 38 l-386 (1978). 23. J. F. C~XLVIEAND J. P. BOUANICH,J. Quant. Spectrosc.Radial. Transfer 27,481-482 (1982). 24. H. S. PEISER(Ed.), Pure Appl. Chem. 56,695-768 (1984). 25. E. R. COHENAND B. N. TAYLOR,J. Phys. Chem. ReJ: Data 2,663-734 (1973). 26. J. K. G. WATSON,J. Mol. Spectrosc.80,411-421 (1980).