Dynamics of H Atom Production from Photodissociation of Acetic Acid-d1

초록

Detailed dissociation dynamics of H(D) from acetic acid-d(1) (CH3COOD) has been investigated upon electronic excitation to the (1)(n,pi*), S-1 state at 205 nm by measuring laser-induced fluorescence spectra of the fragment H(D) atoms. In addition, quantum yields for the H(D) atom dissociation channels, CH3COO + D and CH2COOD + H, were measured, which are 0.07 +/- 0.03 and 0.17 +/- 0.03, respectively. From the Doppler broadened spectra, the center-of-mass translational energy releases into products were obtained. To determine the detailed dissociation dynamics, two-dimensional potential energy surfaces along the reaction coordinate including the coordinate directly coupled to the dissociation coordinate were examined by employing quantum chemical calculations. For the CH3COO + D channel, the coupled coordinate is the dihedral angle of D against the COO plane. The dissociation of D(H) from acetic acid should take place along the triplet surface via surface crossing from the initially excited S-1 state. Along the triplet surface, an exit channel barrier exists, which originates from the structural difference between the T-1 and the product asymptotes, especially the dihedral angle of D against the COO plane. The observed translational energy releases were successfully estimated by the barrier impulsive model based upon the calculated two-dimensional potential energy surfaces at the B3LYP/cc-pVDZ level of theory.

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