Photodissociation of DOBr—Time-dependent wavepacket calculations

Abstract

DOBr photoabsorption cross-sections and product rotational state distributions of the OD fragment resulting from excitation to the two lowest-lying excited singlet electronic states, 1¹A″ and 2¹A′, are computed using time-dependent wavepacket dynamics. The dynamical calculations are based on two-dimensional ab initio potential energy and transition dipole moment surfaces, in which the OD bond length is held fixed. The computed absorption band for DOBr is very similar to that of HOBr for excitation from the ground vibrational state. For vibrationally mediated photofragmentation spectra in which the initial state is a vibrationally excited state, the absorption line shape for DOBr differs markedly from the corresponding HOBr absorption. For all initial vibrational states, the resulting OD fragments are produced more rotationally “hot” than their OH counterparts. The resulting OD and OH rotational distributions agree qualitatively with experimental measurements at 266 nm, where the excitation is dominated by the parallel 2 ¹A′←¹A′ transition. Predictions are also made for the rotational distributions at 355 nm, where the perpendicular transition 1¹A″←¹A′ is dominant and no experimental product state distributions are as yet available.