OBSERVATION OF COMPETING PATHWAYS IN THE RELAXATION OF $ICl^{\ast}$ IN A He SUPERSONIC EXPANSION
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Date
2004
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Ohio State University
Abstract
Collision-induced relaxation of $ICl^{\ast}$ and differing caging mechanisms of electronically excited $ICl^{\ast}$ within $He\cdots ICl^{\ast}$ 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 $ICl(B^{3} \Pi_{0 +}, \nu^{\prime} = 3)$ rotor states occurs on timescales sufficient for vibrational relaxation down to the long-lived $ICl(B,\nu^{\prime} = 2)$ rotor states. It is also shown that when linear $He\cdots ICl(X^{1} \Sigma_{0+}, \nu^{\prime\prime} = 0)$ complexes are promoted to the continuum of states correlating with the repulsive, inner wall of the $ICl(A^{3}\Pi_{1})$ 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 $He\cdots I^{35}Cl(X,\nu^{\prime\prime} = 0)$ complex to intermolecular states associated with the ICl(B) diabat that are coupled with those in the $ICl(B^{\prime})$ adiabat formed by an avoided curve crossing are also observed in laser-induced fluorescence spectra. The $ICl^{\ast}$ molecules within the excited state complex undergoes a non-adiabatic one-atom caging mechanism forming $I^{35}Cl(B,\nu^{\prime})$ products with little rotational excitation.
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Author Institution: Department of Chemistry, Washington University