Spectroscopy of Metastable Species in a Free-Jet Expansion: The β ←ATransition in Br2

✍ Scribed by Eunsook Hwang; Paul J. Dagdigian; Joel Tellinghuisen

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 337 KB
• Volume: 181
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1996.7167

✦ Synopsis

The A 1 u ( 3 P) state of Br 2 is observed in free-jet expansions of UV-photolyzed BBr 3 /Ar mixtures and electrically discharged Br 2 /Ar mixtures. Laser excitation spectra are recorded for the b 1 g ( 3 P 2 ) R A transition, providing the first high-resolution data for £ Å 0 in the A state. Thirteen £-0Љ bands spanning £ Å 23-33 are rotationally analyzed, yielding a total of 475 assignments. The new results are combined with existing spectroscopic data for £ Å 0-10 to yield an improved description of the b state and the following constants (cm 01 ) for £ Å 0 of the A state: TЉ 0 ( 79 Br 2 ) Å 13 984.22(5), TЉ 0 ( 79 Br 81 Br) Å 13 983.80(5), TЉ 0 ( 81 Br 2 ) Å 13 983.32(5), BЉ 0 ( 79 Br 2 ) Å 0.05815(2). The new information for the A state is analyzed together with existing data for levels £ Å 7-24 and 30-34 to achieve compact expressions for the vibronic energy and rotational constant in terms of the standard polynomials in (£ / 1 2 ) at low £, merging smoothly into near-dissociation expansions (NDEs) at high £. The resulting ''mixed representations'' have the usual properties of the polynomials at low £ and yield the estimates (cm 01 , for 79 Br 2 ): T e Å 13 910, D e Å 2147, v e Å 150, B e Å 0.05844, and R e Å 2.704 A ˚. The NDEs have superior extrapolating ability above the highest observed level to dissociation, which occurs at £ D Å 41.7. Spectroscopic constants and RKR potentials are tabulated for the first Ç40 £ levels of both states, and Franck-Condon factors are given for transitions from the low £Љ levels.