Vibrationally Mediated Photolysis Dynamics of H2O in the V^dOH = 3 Manifold: Far Off-Resonance Photodissociation Cross Sections and OH Product State Distributions

Published

May 1, 1999

Author(s)

O Votava, David F. Plusquellic, David Nesbitt

Abstract

Vibrationally mediated photodissociation dynamics of water on the first excited electronic state surface (A) has been studied with slit jet-cooled H₂O prepared in the complete polyad of Ņ_OH=3 overtone stretch levels (l03⁺>, l12⁺>, and l03->). (Notationally, ln₁n₂> refers to symmetric/antisymmetric combinations of local mode OH stretch excitation roughly corresponding to n₁ and n₂ quanta in the spectator and photolyzed OH bond, respectively.) At 248 nm photolysis wavelength the Condon point for bond cleavage occurs in the classically forbidden region, primarily sampling highly asymmetric H+OH exit valley geometries of the potential energy surface. Rotational, vibrational, spin orbit, and lambda doublet distribuions resulting from this far off resonance photodissociation process are probed via laser induced fluorescence, exploiting the high efficiency laser excitation and light collection properties of the slit jet expansion geometry. Only vibrationally unexcited OH products are observed for both l12> and l03> initial excitation of H₂O, despite different levels of vibration in the spectator OH bond. This is in contrast with near-resonance vibrationally mediated photolysis studieds by Crim and co-workers in the l104^-> and l13^-> manifold, but entirely consistent with theoretical predictions from a simple two dimensional quantum model. Photolysis out of the rotational ground H₂O state (I.e.) Jk_aK_c=0₀₀) yields OH product state distributions that demonstrate remarkable insensititivity to the initial choice of H₂O vibrational stretch state, in good agreement with rotational Franck-Condon models. However, this simple trend is not followed uniformly for rotationally excited H₂O precursors, which indicates that these Franck-Condon models are insufficient and suggests that exit channel interactions do play a significant role in photodissociation dynamics of H₂O at the fully state-to-state level.

Citation

Journal of Chemical Physics

Volume

110

Pub Type

Journals

Keywords

H₂O, photodissociation, state-selected dynamics

Citation

Votava, O. , Plusquellic, D. and Nesbitt, D. (1999), Vibrationally Mediated Photolysis Dynamics of H₂O in the V^dOH = 3 Manifold: Far Off-Resonance Photodissociation Cross Sections and OH Product State Distributions, Journal of Chemical Physics (Accessed April 25, 2024)