Laser-pump and probe approach has been applied to the far wings of Hg 3P1 - 1S0 resonance line broadened by collisions with N2 and CO to measure excitation spectra for the formation of Hg(6 3P0) and Hg(6 3P 1). The excitation spectra are highly asymmetric with the red wing being much more extended than the blue wing. The absolute ratio of nascent yields of Hg 3P0 to 3P1 is determined as a function of the excitation wave number. From these measurements, it is found, commonly for Hg-N2 and Hg-CO systems, that (a) the nascent product ratio, Hg(3P0)/Hg(3P 1), grows on the red-wing surface (the A state) with increasing shift, Δv, of the excitation wave number from the line center and finally surpasses unity; (b) the blue-wing surface (the B̃ state) gives mostly Hg(3P1) but has a small chance to give Hg( 3P0). Time constant τ0 for the Ã→3P0 process of Hg-N2 is found to change from 17 to 35 ns as the absorption distance Rc between Hg and N2 changes from 3.6 to 4.7 Å. From these values of τ0, the transition probability P(Ã→3P 0) for a single approach of Hg-N2 to the turning point region is estimated to be about 3.7×10-5. The transition probability P(B̃→3P0) is about 270 times larger than P(Ã→3P0). CO is about 20 times more effective than N2 for the B̃3P0 process. The Rc dependence of τ0 can be qualitatively explained by the vibrational frequencies of the bound Ã state and the Franck-Condon factor between the bound Ã state and the free (repulsive) ã state arising from Hg(3P0)+N2. These findings suggest that the direct Ã→ã transition is realized in these Hg-N 2 and Hg-CO collisions. This gives a remarkable contrast to Hg-atom collisions, where the A→3P0 process is parity-forbidden due to the 0+ and 0- characters of the A and a states, respectively. The coupling mechanisms for the Ã→ã and B̃→ã transitions in Hg-N2 collisions are discussed in detail. The theoretical estimate of the Ã→ã transition probability is made to be compared with the experimental value.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry