Velocity dependence of rotationally inelastic collisions: 7Li2(A 1Σ) +Ne, Ar, and Xe

We present velocity-selected measurements of the cross sections for rotationally inelastic collisions of 7Li(2(A 1Σ) with Xe, Ar, and Ne, with various pairs of initial and final rotational levels, j/sub i/ and j/sub f/: Li(2(v/sub i/ = 9, j/sub i/) +X→Li(2(v/sub f/ = 9, j/sub f/ = j/sub i/+Δ)+X. For each target gas measurements were made with j/sub i/ = 8, 22, and 42 for approximately eight values of Δ with an overall range of -20 to +24; a total of 69 cross sections were measured. Velocity selection is accomplished by a Doppler-based laser-selection technique combined with further numerical inversion methods. We achieve a measurable relative velocity range of approx. =0.5→3 x 105 cm/s, corresponding to kinetic energies of 120 to 3500 K. In contrast to the few previous similar studies, our data show a dramatic and varied velocity dependence. We have observed a few cross sections which increase substantially with velocity, some which rise faster than v-1/sub r/ at low velocity, some that fall like v-2/sub r/ at high velocity, and numerous examples of peaks in endoergic cross sections near threshold. We have seen two distinct types of rotationally adiabatic reduction in certain cross sections: Vertical BarΔVertical Bar = 2 in Li(2--Xe and j/sub i/ = 42, Δ< or approx. =-16, in all three systems, particularly in Li(2--Ne