CONTINUUM ABSORPTION-SPECTRA IN THE FAR WINGS OF THE HG S-1(0)-]P-3(1) RESONANCE LINE BROADENED BY AR

Absolute reduced absorption coefficients for the Hg resonance line at 253.7 nm broadened by Ar were determined between 390 and 430 K in the spectral range from 20 to 1000 cm(-1) on the red wing and from 20 to 4 00 cm(-1) on the blue wing. The resultant reduced absorption coefficie nts are in fair agreement with those obtained by Petzold and Behmenbur g [Z. Naturtorsch. Tell A 33, 1461 (1978)]. The observed A (3)0(+) <-- X (1)0(+) spectrum in the spectral range from 80 to 800 cm(-1) on the red wing agrees remarkably well both in shape and magnitude with the quasistatic line shape calculated using the potential-energy curves of the HgAr van der Waals molecule given by Fuke, Saito, and Kaya [J. Ch em. Phys. 81, 2591 (1984)], and Yamanouchi et al. [J. Chem. Phys. 88, 205 (1988)]. The blue-wing spectrum is interpreted as the B (3)1 <-- X (1)0(+) free-free transition of HgAr by a simulation of the spectrum using uniform semiclassical treatment for the free-free Franck-Condon factor. The source of the satellites on the blue wing is attributed to the phase-interference effect arising from a stationary phase-shift d ifference between the B- and X-state translational wave functions. The stationary phase-shift difference arises owing to the existence of a maximum in the difference potential between the B and X states. The re pulsive branches of the potential-energy curves of HgAr for the X and B states have been revised to give excellent agreement between the obs erved and calculated spectra, both in shape and magnitude.