Theoretical Study of Photoassociation of Alkali-Metal Dimers

Abstract

The photoassociation of alkali metal molecules (Rb₂, Cs₂, and RbCs) at short range is investigated in theory. Based on ab initio calculations to rationalize Franck–Condon filtering, the target states of photoassociation have been obtained. They correspond to vibrational transition levels from excited state (Rb₂: ${v}{\kern 1pt} '$ = 17–21, Cs₂: ${v}{\kern 1pt} '$ = 21–25, and RbCs: ${v}{\kern 1pt} '$ = 18–22) to ground state. By using quantum wave-packet dynamic methods, the yields with time evaluation of the selected states are calculated interacting with a resonant laser pulse. Using gaussian pulse leads to the yield of Rb₂ up to 82% at 860 fs. After a laser pulse, the positive chirp promotes the yield of vibrational states to increase, but the negative chirp inhibits it. That is to say, by changing the laser parameters and pulse shapes, it is much easier to control the photochemical process along desired direction. For photoassociation of alkali-metal dimers, homonuclear molecules have a better response to laser pulse than heteronuclear molecules. The efficiency of photochemical reaction of homonuclear molecules is much better and the photoassociative yield is much higher. Those conditions will provide an important reference and suggest a scheme for a feasible photoassociation for further experimental and theoretical research.