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

Abstract

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 SO 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.