New trends in the state-to-state photodissociation dynamics of H2O(Ã)

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The water molecule, rotationally state selected in the third and fourth OH stretching overtone (‖04〉−, ‖05〉−) and stretch–bend combination (‖04−2〉) levels, has been photodissociated via the à state at λ≂282 nm. The photofragment rotational state distributions, determined by OH(A–X) laser induced fluorescence (LIF), differ from those reported previously by Andresen and co-workers, in which water was initially prepared in the ‖01〉− level and photodissociated at 193 nm, and from those by Crim and co-workers, in which H2O was photodissociated via the ‖04〉− level at wavelengths shorter than 282 nm. These differences become more pronounced with increasing angular momentum in the parent water molecule and with an increasing number of quanta in the intermediate OH stretching overtone state. The Franck–Condon theory of Balint-Kurti, previously employed successfully to account for the product state distributions arising from the 193 nm photodissociation of H2O‖01〉−, qualitatively reproduces the trends observed in the present study if it is assumed that dissociation occurs preferentially from extended RH-OH configurations of the ‖04〉− and ‖05〉− overtones. The product OH state distributions are thus shown to be sensitive indicators of the bending and rotational motions of H2O(X̃) in the wide amplitude stretching region of the ground state surface.