Three-state surface hopping calculations of acetaldehyde photodissociation to CH3 + HCO on ab initio potential surfaces

We report Trajectory Surface Hopping (TSH) calculations of CH3CHO photodissociation involving three electronic states, S-1, T-1, and S-0, with a focus on the radical products CH3 + HCO, which can be formed from both T-1 and S-0. We use previously reported potential energy surfaces and spin-orbit couplings for T-1 and S-0 and report a new potential and spin-orbit coupling for S-1 here. Roughly 32 000 trajectories are performed at energies corresponding to seven photolysis wavelengths between 372 and 230 nm. Motivated by recent experiments, we examine the branching ratio of the T-1 to S-0 pathways as a function of photolysis energy. We also present the relative translational energy and CH3 vibrational energy distributions from these pathways at a photolysis energy of 100 kcal mol(-1), formed from both the T-1 and S-0 potentials. As with standard quasiclassical trajectory calculations, violation of zero-point energy for products also occurs in TSH calculations. This is shown to be a serious issue for this branching ratio and one of several methods considered to deal with this issue is shown to give satisfactory results.