Dynamics of H Atom Production from Photodissociation of Acetic Acid-d(1)

Detailed dissociation dynamics of H(D) from acetic acid-d1 (CH3COOD) has been investigated upon electronic excitation to the (1)(n,π*), S1 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 S1 state. Along the triplet surface, an exit channel barrier exists, which originates from the structural difference between the T1 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.