Isotopic effects on SO2 photolysis; a theoretical study for rotational resolved spectra and its consequences for atmospheric self-shielding

Sulfur dioxide (SO₂) is one of the many trace gases present in the atmosphere. The photodissociation reaction by UV light initiates a complicated oxidation process which its final product sulfates and sulfuric acid form aerosols. This chemical process is complemented by physical deposition which brings back sulfate aerosols to earth to become part of the soil and rocks. The photodissociation process is assumed to imprint a characteristic isotopic fractionation highly dependent on wavelength therefore the sulfates contained in rocks from different geological ages would have a characteristic isotopic fractionation of the atmospheric radiactive conditions of that age. Previously recorded UV absorption spectra of ³²SO₂, ³³SO₂, ³⁴SO₂ (Danielache et al., 2008) have been used to interpret the geological record. Due to UV shielding, atmospheric concentrations of O₂, O₃, OCS, ₂, H₂O, and SO₂ influence on isotopic fractionations and contribute to the mass independent fractionation (MIF) observed in rocks from the beginning of earth up to 2.4 billion years before present, also called Archaean MIF (Ueno et al., 2009).In this study we report ^32,33,34&36SO₂ spectra calculated wavepacket dynamics with a newly developed method that take into account non-adiabatic transitions, furthermore the implemented methodology has been constructed to reproduce a, yet to be measured, rotationally resolved spectra and by optimizing the absorption width of each transition to the Doppler limit and its pressure variation we construct spectra suitable to specific atmospheric conditions. The obtained data sets opens the enable us to study self-shielding mechanisms for a wide range of scenarios.