New experimental evidences for dynamical constraints on angular momentum transfer in heavy molecules–light particles collisions: I*2(B)+4He, 3He, H2, D2

The selective laser excitation and induced fluorescence observation technique has been used to study thermally averaged rotationally inelastic processes: I*2 (B, vi=15, ji)+M→I*2 (B,vi=15, jf )+M with M=4He, 3He, H2, D2. In each case, the transfer rates k( ji→jf) display an exponential-like dropoff vs ‖ jf−ji‖, confirming the importance of dynamical constraints on the transfer of angular momentum by light particles. The onset of this sharp decrease scales like the relative linear momentum of the colliding particles and might be interpreted as resulting from a rotational rainbow effect. Effective anisotropies for I*2 –He and I*2 –H2 potential energy surfaces can thus be estimated.