Molecular dynamic simulations of OH-stretching overtone induced photodissociation of fluorosulfonic and chlorosulfonic acid

We investigate the OH-stretching overtone dynamics of fluorosulfonic acid (FSO3H) and chlorosulfonic acid (ClSO3H) using classical trajectory simulations. The initial nuclear coordinates and momenta for the trajectories are sampled from anharmonic correlation-corrected vibrational self consistent field (CC-VSCF) wavefunctions. We consider both OH-stretching overtone states and combination states containing a mix of OH-stretching overtones and SOH-bending or OSOH-torsional modes. Our molecular dynamics simulations confirm that photodissociation of these sulfonic acids to form the corresponding hydrogen halides and sulfur trioxide (HF + SO3 and HCl + SO3), is possible via highly vibrationally excited states on a picosecond timescale. Hydrogen-hopping events are also observed in the trajectories whereby the hydrogen atom of the excited OH group is found to migrate to one of the adjacent S=O groups. The transition states, activation energies and dissociation dynamics of FSO3H and ClSO3H are found to be similar to those of H2SO4. We suggest that these halogenated sulfonic acids should be suitable proxy molecules for an experimental investigation of the OH-stretching overtone induced photodissociation of H2SO4 thought to be important in Earths' atmosphere.