The role of the rotational state in iIntermolecular iInteractions of H2O with H2 and CH3Cl

Rotational-state resolved naeasurements or H,O I-1, and H_,O CfI~CI iIntermolecular iInteractions were pcrlbrmed. Using light-induced drift as a tool. we measured changes in transport collision rate v upon ro~ibrational I J, tʹbexcitation of H,O. We studied P- and R-branch excitation with J ranging from 0 through 9 Ibr H,O excited in the fundanlcntal asymmetric stretch mode. Combination of P and R data yields the dependencies of v upon rotational IJI and vibrational (rl quantum nunabers separately. For H_,O-CH~CI it is Iound that v decreases hy 25 % as J increases fronx 0 to 9. For H_,O-H, the decrease is only 1.0".<,. These data seem to exenaplify a fundamental aspect of dipole dipole iInteraction: the familiar I r ʹ iInteraction term is highly J-dependent. This is attributed to the increasing averaging-out of the dipolar potential as the rotational qu;.intu131 nunlber increases.