Ricerc@Sapienza

Gas phase ion chemistry has fundamental and applicative purposes since it allows the study of the chemical processes in a solvent free environment and represents models for reactions occurring in the space at low and high temperatures. In this work the ion-molecule reaction of sulfur dioxide ion SO.+2 with carbon monoxide CO is investigated in a joint experimental and theoretical study.

SO2 has been proposed in solar geoengineering as a precursor of H2SO4 aerosol, a cooling agent active in the stratosphere to contrast climate change. Atmospheric ionization sources can ionize SO2 into excited states of (Formula presented.), which quickly reacts with trace gases in the stratosphere. In this work we explore the reaction of (Formula presented.) with (Formula presented.) excited by tunable synchrotron radiation, leading to (Formula presented.) ((Formula presented.)), where H contributes to O3 depletion and OH formation.

The reaction dynamics and the temperature-dependent kinetic trend of the SO2.+ion-molecule reactions with water and methane have been studied using the tunable synchrotron radiation to produce excited SO2.+ions and ab-initio methods. The experimental results show that only one product, HSO2+, is formed in both reactions and its yield displays different trends with the photon energy. DFT and VTST calculations have been used to explore the dynamics of the reactions and to calculate the rate constants at different temperatures.