Vibrationally Induced Dissociation of Sulfuric Acid (H₂SO₄)

One of the important reactive steps in Earth’s atmosphere is the decomposition of H2SO4 to H2O and SO3. However, because the UV spectrum of H2SO4 was not found up to 140 nm, alternative mechanisms, including vibrationally induced dissociation, were proposed. Using adiabatic reactive molecular dynamics (ARMD) simulations with validated force fields for the product and educt channels, it is shown through explicit atomistic simulation that by exciting the ν9 (OH-stretching-) mode, photodissociation can occur on the picosecond time scale. With the potential energy surfaces used in the present work, ν9 = 4 is sufficient for this process. From a statistically significant number of trajectories (several thousands), vibrationally induced dissociation times are found to follow Gamma-distributions with most likely reaction times between 40 and 200 ps by depositing energies ranging from 40 to 60 kcal/mol, corresponding to 4 and 6 vibrational quanta in the OH stretching vibration. Because ARMD simulations allow multiple and long-time simulations, both nonstatistical, impulsive H-transfer and statistical, IVR-regimes of the decomposition reaction can be discussed in detail at an atomistic level.