Dynamics of vibrational overtone excitations of H₂SO ₄, H₂SO₄-H₂O: Hydrogen-hopping and photodissociation processes

Photochemical processes of sulfuric acid (H₂SO₄) and sulfuric acid monohydrate (H₂SO₄-H₂O) following overtone excitation of the OH stretching mode are studied by classical trajectory simulations using the semiempirical PM3 potential suface in "on the fly" calculations. The main results arse the following: (1) In the excitation of H₂SO₄ to the fifth OH-stretch overtone, hopping of the H atom between oxygen atoms is found to take place in 22% of the trajectories, only once during simulations of 400 ps. (2) All the trajectories for H₂SO₄ show a rapid cis-trans isomerization. (3) The photolysis of H₂SO₄ into SO₃ + H₂O takes place in 5% of the trajectories on a time scale of ∼9 ps. (4) Only low overtone levels of H₂SO₄-H₂O have sufficiently long lifetimes to be spectroscopically relevant. Excitation to these OH stretching overtones is found to result in the dissociation of the cluster. H hopping or dissociation of H₂SO₄ does not take place.