P. Colarusso et al- High-Resolution Infrared Emission Spectrum of Strontium Monofluoride

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OURNAL OF MOLECULAR SPECTROSCOPY 175, 158171 (1996)

ARTICLE NO. 0019

High-Resolution Infrared Emission Spectrumof Strontium Monofluoride

P. Colarusso, B. Guo, K.-Q. Zhang, and P. F. Bernath

Centre for Molecular Beams and Laser Chemistry, Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

Received August 16, 1995; in revised form October 10, 1995

The high-resolution infrared spectrum of gas-phase SrF was obtained in emission with a Fourier transformspectrometer. Approximately 1400 rotational lines from the 10 to the 87 bands were measured in the X2S/

ground state of the major isotopomer, 88SrF. The Dunham coefficients Yl,m have been derived from a combined fitof the infrared transitions with microwave transitions that have been previously reported in the literature. 1996Academic Press, Inc.

INTRODUCTION investigated by Azuma and co-workers (16). The dipole mo-

ments of the X2S/ ground state as well as the A2P and B2S/

The first quantum mechanical interpretations of the band excited states of 88SrF have been determined using Starkpectra of SrF date back at least to the 1920s (1, 2). Subse- measurements (17, 18).

quent reports identified electronic bands in emission spectra Recently, our laboratory has investigated the infraredrom carbon arcs and discharges (3, 4) as well as in absorp- emission spectra of MgF (19), CaF (20), and BaF (21). Inion spectra (3, 5). In these early studies, the analysis was this study, we report the analysis of the infrared emissionimited to the vibrational structure because the electronic spectrum of SrF.pectra of SrF are extremely congested.

EXPERIMENTAL DETAILSThe first rotational analysis of SrF was reported by

Barrow and Beale in 1967; they recorded and analyzedGas-phase SrF was produced by reacting a mixture of Sr

he high-resolution spectrum of the 0 0 band of themetal and SrF2 in a high-temperature furnace. The reactanF2S/ X2S/ transition (6). This work was followed by

everal laser spectroscopic experiments. Steimle et al.ecorded and analyzed the (0, 0), (1, 1), and (2, 2) bands TABLE 1of the B2S/ X2S/ transition (7). The same electronic Molecular Constants for 88SrF (in cm01)*ransition was studied at sub-Doppler resolution using

ntermodulation fluorescence spectroscopy (8) as well as

polarization spectroscopy (9). The (1, 0) and (2, 1) bands

of the A2PX2S/ transition were studied by laser excita-

ion of SrF in a low-pressure flame (10); more recently,

he (0, 0) band has been studied using molecular beam

echniques (11). Nitsch et al. used opticaloptical double

esonance to investigate the F2S/ and G2P states via the

ntermediate B2S/ state (12).

The spectra of SrF have also been studied in the micro-wave and millimeter-wave regions. Domaille et al. used mi-

crowave optical double resonance in order to measure sev-

eral pure rotational transitions of88SrF in the X2S/ state (13).

Schutze-Pahlmann and co-workers obtained the rotational

pectrum of 88SrF using millimeter-wave absorption; they

determined some of the Dunham coefficients as well as

pinrotation constants (14). Childs and co-workers deter-

mined the spinrotation constants and the isotropic and an-

sotropic hyperfine constants for 88SrF and 86SrF (15). The

hyperfine structure of 87SrF in the ground state has been

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IR SPECTROSCOPY OF SrF 159

FIG. 1. A portion of the emission spectrum of SrF. The R-branch lines of the 10 to the 54 vibrational bands are marked along with the N values

mixture was placed in the center of an alumina tube con- dows at both ends. In order to avoid deposition on the win

dows, 30 Torr of argon was introduced into the tube. Theaining a carbon liner. The center portion of the tube was

housed in the furnace, which was heated to 1650C at a rate infrared emission was directed from one end of the tube into

a port of a Bruker IFS 120 HR Fourier transform spectrome-of 5 /min. The alumina tube was sealed with KRS-5 win-

ter. The emission spectrum of SrF was recorded at a resolu-

tion of 0.01 cm01 with a helium-cooled Si:B detector overTABLE 2 the spectral region ranging from 350 to 750 cm01.

Dunham Coefficients of 88SrF*

RESULTS AND ANALYSIS

While Sr has five naturally occurring isotopes (84SrF

(0.56%), (86Sr (9.86%), 87SrF (7.00%), and 88SrF (82.58%)

(22), only 88SrF was detected in this experiment. The line

positions were measured using Braults PC-DECOMP, a

computer program that fits a spectral lineshape to a Voig

lineshape function. Spin rotation splitting was not resolved

HF lines, which were present in the spectrum as an impurity

were used in the absolute calibration of the 88SrF spectrum

(23). The line positions were organized into different bands

using an in-house program based on the Loomis Woodtechnique. The 1 0 and 2 1 bands were assigned using

combination differences based on the data reported by

Steimle et al. (7). The line positions were then fit to the

standard energy level expression

F,N T / BN(N/ 1) 0 D[N(N/ 1)]

2

[1

/ H[N(N/ 1)]3.

The preliminary constants were used to assign the next few

Copyright 1996 by Academic Press, Inc.


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COLARUSSO ET AL.160

TABLE 3

Observed and Calculated Transition Wavenumbers (in cm01)

1 Observed 0 Calculated (in 1103 cm01).



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TABLE 3 Continued

vibrational bands in an iterative procedure. In all, approxi- ACKNOWLEDGMENT

mately 1400 lines were assigned from the 10 to the 87The authors thank the Natural Science and Engineering Research Councibands. These line positions, as well as millimeter-wave data

of Canada (NSERC) for the support of this research.rom the work of Schutze-Pahlmann and co-workers (14),

were included in the final fit to Eq. [1]. Vibrational termREFERENCESenergies and rotational constants are listed in Table 1. A

portion of the emission spectrum of SrF is shown in Fig. 1.1. R. Mecke, Z. Phys. 42, 390 425 (1927).The observed frequencies and the pure rotational data2. R. C. Johnson, Proc. R. Soc. London A 122, 161 188 (1929).

were also fit to the energy levels of the Dunham model: 3. A. Harvey, Proc. R. Soc. London A 133, 336350 (1931).4. M. M. Novikov and L. V. Gurvich, Opt. Spectrosc. 22, 395399 (1967)

F,N

l,m

Yl,m( /12)

l[N(N/ 1)]m. [2] 5. C. A. Fowler, Phys. Rev. 59, 645 652 (1941).6. R. F. Barrow and J. R. Beale, Chem. Commun. 12, 606 (1967).

7. T. C. Steimle, P. J. Domaille, and D. O. Harris, J. Mol. Spectrosc. 68The Dunham Yl,m constants are given in Table 2. All of the 134145 (1977).

8. J. M. Brown, D. J. Milton, and T. C. Steimle, Discuss. Faraday Socmeasured line positions are listed in Table 3.71, 151 163 (1981).In summary, infrared emission spectroscopy is an effec-

9. W. E. Ernst and J. O. Schroder, Chem. Phys. 78, 363368 (1983).ive technique for obtaining the spectra of the alkaline earth10. T. C. Steimle, P. J. Domaille, and D. O. Harris, J. Mol. Spectrosc. 73

monofluorides. The infrared emission spectrum of the major441443 (1978).

sotopomer of SrF has been analyzed and the spectroscopic 11. T. C. Steimle, D. A. Fletcher, and C. T. Scurlock, J. Mol. Spectrosc158, 487 488 (1993).constants have been presented.



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2. C. Nitsch, J. O. Schroder, and W. E. Ernst, Chem. Phys. Lett. 148, 18. J. Kandler, T. Martell, and W. E. Ernst, Chem. Phys. Lett. 155, 470

474 (1989).130135 (1988).19. B. E. Barber, K.-Q. Zhang, B. Guo, and P. F. Bernath,J. Mol. Spectrosc3. P. J. Domaille, T. C. Steimle, and D. O. Harris, J. Mol. Spectrosc. 68,

169, 583 589 (1995).146155 (1977).20. F. Charron, B. Guo, K.-Q. Zhang, Z. Morbi, and P. F. Bernath, J. Mol4. H.-U. Schutze-Pahlmann, Ch. Ryzlewicz, J. Hoeft, and T. Torring,

Spectrosc. 171, 160168 (1995).Chem. Phys. Lett. 93, 7477 (1982).21. B. Guo, K. Q. Zhang, and P. F. Bernath, J. Mol. Spectrosc. 170, 59

5. W. J. Childs, L. S. Goodman, and I. Renhorn, J. Mol. Spectrosc. 87,74 (1995).

522533 (1981).22. I. Mills, T. Cvitas, K. Homann, N. Kallay, and K. Kuchitsu, Quanti

6. Y. Azuma, W. J. Childs, G. L. Goodman, and T. C. Steimle, J. Chem.ties, Units, and Symbols in Physical Chemistry, Blackwell Sci

Phys. 93, 55335538 (1990).Oxford, 1988.

7. W. E. Ernst, J. Kandler, S. Kindt, and T. Torring, Chem. Phys. Lett. 23. R. B. LeBlanc, J. B. White, and P. F. Bernath, J. Mol. Spectrosc. 164113, 351354 (1985). 574579 (1994).

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P. Colarusso et al- High-Resolution Infrared Emission Spectrum of Strontium Monofluoride