A. Muntianu, B. Guo and P. F. Bernath- High-Resolution Infrared Emission Spectrum of NaF

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OURNAL OF MOLECULAR SPECTROSCOPY 176, 274– 279 (1996)

ARTICLE NO. 0087

High-Resolution Infrared Emission Spectrum of NaF

A. Muntianu, B. Guo, and P. F. Bernath

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

Received September 25, 1995; in revised form December 4, 1995

The high-resolution infrared emission spectrum of sodium monofluoride has been recorded with a Fourier transformspectrometer. A total of 1131 of vibration–rotation transitions, from the £ Å 1 r 0 to £ Å 9 r 8 vibrational bands,have been assigned. The infrared data have been combined with existing microwave data in order to obtain improvedspectroscopic constants, including Dunham Y ij and U ij coefficients, for the X 1S/ electronic ground state of NaF. 1996

Academic Press, Inc.

INTRODUCTION An electron diffraction study of alkali fluoride vapors (5)has also been completed. In addition, it should be men-

Alkali halides are the classical examples of ionic bond- tioned that the spectroscopic constants of NaF are use-

ng. These molecules have been extensively studied by ful in the study of reaction dynamics, such as the Na /many different methods. A review of the spectroscopic FCH3 r NaF / CH3 system (6 ). This paper represents theiterature on NaF was published by Douay et al. (1) in first experimental study and analysis of the high-resolu-heir diode laser measurements of the vibration–rotation tion Fourier-transform infrared emission spectrum of NaF.

first overtone spectrum. Since that time, some ab initio The previous diode laser work (1) generated a very smallcalculations have been published (2, 3), as well as a refit data set since only a few R-branch lines were measuredof the NaF data using analytical potential functions ( 4). for the D £ Å 2 overtone bands.

FIG. 1. A portion of the R branch of vibration–rotation spectrum of NaF. The 1–0 and 2–1 bands are marked along with the J value.

274022-2852/96 $18.00

opyright 1996 by Academic Press, Inc.

All rights of reproduction in any form reserved.

AID JMS 6 50 / 6t0 421 03-18- 6 20:55:45 ms al AP: Mol S ec



INFRARED EMISSION OF NaF 275

TABLE 1

Observed Rovibrational Line Positions of the X 1S/ State of NaF in cm01 [Observed 0 Calculated Values Are Shown

in the Column Labeled D (in units of cm01)]

Copyright 1996 by Academic Press, Inc.

AID JMS 6 50 / 6t0 6 50 03-18- 6 20:55:45 ms al AP: Mol S ec



MUNTIANU, GUO, AND BERNATH276

TABLE 1 —Continued

EXPERIMENTAL DETAILS heating NaF powder in a commercial CM Rapid Temp

Furnace. The NaF powder was placed in the central part

The high-resolution infrared emission spectrum of NaF of a mullite (3Al2O3r2SiO2) tube; its interior was pro-

has been recorded with a Bruker IFS 120 HR Fourier tected by a carbon liner tube. The tube was heated slowly

in order to prevent the cracking of the tube. The cell wasransform spectrometer. Gas-phase NaF was obtained by






TABLE 1 —Continued

TABLE 2

Spectroscopic Constants for the X 1S/ Ground State of NaF (in cm01)


AID JMS 6 50 / 6t0 6 50 03-18- 6 20:55:45 ms al AP: Mol S ec



MUNTIANU, GUO, AND BERNATH278

TABLE 3 position of the lines was calibrated in accordance withDunham Y ij Coefficients for the X

1S/ Ground State of NaF the strong pure rotational HF lines (8) that appeared in

the spectrum. Nine vibrational bands from £ Å 1 r 0 to

£ Å 9 r 8 were observed and the lines positions are

reported in Table 1. In order to obtain improved spectro-

scopic constants for NaF that can describe both the infra-

red and microwave data, all of the lines reported in Table

1 were fitted together with three microwave transitions

(9) and ten millimeter-wave transitions (10). The diodelaser measurements (1) were not included, since the pres-

ent measurements should be superior in precision. The

customary spectroscopic constants for the X 1S/ ground

state of NaF are given in Table 2. A reduced standard

TABLE 4

Dunham U ij Coefficients for the X 1S/

Ground State of NaF

pumped to remove the impurities up to a temperature of

approximately 800C. Above this temperature, the pump-

ng port was sealed and about 5 Torr of argon buffer gas

was added to prevent deposition of material onto the cell

windows. In this type of experiment, a partial pressureof about 1 Torr of the high-temperature gas-phase mole-

cule is desirable in order to obtain a high signal-to-noise

atio. The NaF partial pressure is 1 Torr at 1077C (7 ),

o the spectrum was recorded at 1100C and the signal-

o-noise ratio was approximately 15:1. The resolution of

he spectrum was 0.005 cm01 over the range 400–750

cm01. A liquid-helium-cooled Si:B detector, a KBr beam-

plitter, and KRS-5 cell windows were used. The final

ecording consisted of 50 coadded scans. A portion of

he spectrum showing part of the R branches of the 1–0

and 2–1 bands with the J value marked is displayed in

Fig. 1.

RESULTS AN D DISCUSSION

A total of 1131 transitions was observed and analyzed.

The line positions were measured using the PC-Decomp

program. This program, developed by J. Brault, deter-

mines the line centers by fitting the measured line profiles

o Voigt lineshape functions. The assignment of the bands

was carried out using an interactive color Loomis–Wood

program. The assignment of the rotational lines was based

on the previous constants found in the literature ( 1). The






deviation of the fit of 0.587 was obtained with 38 parame- ACKNOWLEDGMENT

ers.We thank the Natural Sciences and Engineering Research Council of

Dunham Y ij coefficients, listed in Table 3, were obtained Canada for support.

by fitting the data set to the energy level expression (11)REFERENCES

1. M. C. Douay, A. M. R. P. Bopegedera, C. R. Brazier, and P. F. Bernath,

Chem. Phys. Lett. 148, 1–5 (1988).

2. J. Modisette, L. Lou, and P. Nordlander, J. Chem. Phys. 101, 8903– E ( £, J ) Å ∑i, j

Y ij £ / 1

2i [ J ( J / 1)] j.

8907 (1994).

3. I. Garcı Ba-Cuesta, L. Serrano-Andres, A. Sanchez de Meras, and I.

Nebot-Gil, Chem. Phys. Lett. 199, 535– 544 (1992).

4. J. A. Coxon and P. G. Hajigeorgiou, Chem. Phys. 167, 327– 340 (1992).

5. J. G. Hartley and M. Fink, J. Chem. Phys. 89, 6058–6063 (1988).A total of 14 Dunham Y ij constants were necessary to repro-6. J. C. Polanyi, J. X. Wang, and S. H. Yang, Israel J. Chem. 34, 55–58duce the data with a reduced standard deviation of 0.539.

(1994).These constants are in agreement with, but superior to, those

7. D. R. Lide (Ed.), ‘‘Handbook of Chemistry and Physics,’’ 74th ed.eported by Douay et al. (1). Finally, to minimize the number CRC Press, Boca Raton, FL, 1993.

of free parameters, a mass-reduced Dunham fit (mNa Å 8. R. B. Le Blanc, J. B. White, and P. F. Bernath, J. Mol. Spectrosc. 164,

574–579 (1994).22.98977, mF Å 18.998403) was carried out, varying only9. R. K. Bauer and H. Lew, Can. J. Phys. 41, 1461–1469 (1963).he U i0 and U i1 constants (12). All higher order U ij ( j ú 1)

10. S. E. Veazey and W. Gordy, Phys. Rev. A 138, 1303–1311 (1965).constants were constrained by analytical relationships (12).

11. J. L. Dunham, Phys. Rev. 41, 721–731 (1932).n this case, nine parameters reproduced the data with a 12. H. G. Hedderich, M. Dulick, and P. F. Bernath, J. Chem. Phys. 99,

8363–8370 (1993).tandard deviation of 0.741 (see Table 4).


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