Theoretical study of ultraviolet induced photodissociation dynamics of sulfuric acid

- Photodissociation dynamics of H2SO4 at low-lying electronically excited states were investigated.
- Photochemical processes were simulated by on-the-fly ab initio MD.
- Sulfuric acid after the excitation to the S1 state dissociated to HSO4(12A″) + H(2S).
- Sulfuric acid after the excitation to the S2 state dissociated to HSO4(22A″) + H(2S).
- The energy region of the UV spectra where NMD fractionation may occur is predicted.

Photodissociation dynamics of sulfuric acid after excitation to the first and second excited states (S1 and S2) were studied by an on-the-fly ab initio molecular dynamics simulations based on the Zhu-Nakamura version of the trajectory surface hopping (ZN-TSH). Forces acting on the nuclear motion were computed on-the-fly by CASSCF method with Dunning's augmented cc-pVDZ basis set. It was newly found that the parent molecule dissociated into two reaction-channels (i) HSO4(12A″) + H(2S) by S1-excitation, and (ii) HSO4(22A″) + H(2S) by S2-excitation. The direct dissociation dynamics yield products different from the SO2 + 2OH fragments often presented in the literature. Both channels result in the same product and differs only in the electronic state of the HSO4 fragment. The trajectories running on S2 do not hop with S0 and a nonadiabatic transition happens at the S2-S1 conical intersection located at a longer OH bond-length than the S1-S0 intersection producing an electronic excited state (22A″) of HSO4 product.