15min:

JOSHUA P. DARR AND RICHARD A. LOOMIS, Department of Chemistry, Washington University, One Brookings Drive, CB 1134, Saint Louis, MO 63130.

Collision-induced relaxation of ICl* and differing caging mechanisms of electronically excited ICl* within He ICl* complexes are investigated using laser-induced fluorescence and two-laser, pump-probe spectroscopy. It is found that collisions of He atoms with molecules prepared in the short-lived ICl( B ³ ₀₊, v '=3) rotor states occurs on timescales sufficient for vibrational relaxation down to the long-lived ICl( B , v '=2) rotor states. It is also shown that when linear He ICl( X ¹ ₀₊, v ''=0) complexes are promoted to the continuum of states correlating with the repulsive, inner wall of the ICl( A ³ ₁) potential, the dissociating ICl( A ) molecule undergoes kinematic one-atom caging, ejecting the weakly bound He atom, and re-stabilizing the molecule in high lying vibrational levels within the A electronic state with very little rotational excitation. Features associated with transitions of the linear He I³⁵Cl( X , v ''=0) complex to intermolecular states associated with the ICl( B ) diabat that are coupled with those in the ICl( B ') adiabat formed by an avoided curve crossing are also observed in laser-induced fluorescence spectra. The ICl* molecules within the excited state complex undergoes a non-adiabatic one-atom caging mechanism forming I³⁵Cl( B , v ') products with little rotational excitation.