Evidence for Rb-Rare-Gas Molecules from the Relaxation of Polarized Rb Atoms in a Rare Gas. Theory

Relaxation experiments performed on optically polarized Rb atoms in a rare gas have been previously reported; their detailed interpretation is given below. It is shown that the relaxation governed by the spin-orbit interaction is strongly affected by the formation of chemically unstable Rb-Kr molecules bound by van der Waals forces. Two processes of molecule formation are analyzed: binary resonant collisions leading to metastable states and three-body collisions producing actual bound states. A relaxation model valid for any disorientation probability per single Rb-Kr interaction is developed. Aside from clear evidence for the existence of alkali-rare-gas molecules, the success of the theoretical interpretation of the relaxation experiments yields the equilibrium constant K=1. 710^-22 cm^3/molecule for the reaction Rb+Kr Rb-Kr at 300^, the average lifetime of a Rb-Kr molecule in the gas phase, =0. 6510^-7 sec, at a krypton pressure of one Torr, and the average spin-orbit coupling constant in a Rb-Kr molecule, h^-1=0. 63 MHz. It is also shown that the spin-orbit potential is predominantly short-range.