Surface species formed during UV photolysis of ozone adsorbed on water ice films at 80 K. A combined RA-FTIR and DFT study
The reflectionabsorption FTIR spectra of the ozonewater films deposited on a cold metallic surface at 80 K beforeand after irradiation at 250 and 320 nm were studied to model the ozone photolysis and superoxidant adsorptiontaking place on the ice particles in the Earth's atmosphere. A new sharp intense band at 2860 cm1 and a low-intenseband at 1450 cm1 were observed after irradiation at both wavelengths together with remarkable reshaping of the iceIh bands in the regions 31003600 cm1 and 5001000 cm1. The annealing of the reaction mixture has small effecton the intensities and positions of the new bands. The adsorption of formed species was modelled by DFT clustercalculations. The species O(1D), O(3P), O2, HO, HOO, H2O2 were considered as possible intermediates and products.Among them, HO, H2O2, and HOO, form hydrogen bound complexes with estimated binding energies of 17.6, 28.5,and 37.2 kJ mol1, correspondingly. The observed IR band of 2860 cm1 can not be assigned to the OH vibrations ofH2O2 shifted due to the adsorption and it is assigned to the combination band of H2O2. Apart from H2O2, twoother species can absorb in the region 27002900 cm1: the adsorption complex of HOO on the ice surface and O(1D)forming the complex with the ice of oxywater structure O--OH2 stabilized by additional hydrogen bonds.