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