Direct observation of OH radicals ejected from water ice surface in the photoirradiation of nitrate adsorbed on ice at 100 K

Production of gaseous OH radicals in the 248-350 nm photoirradiation of NO^3- doped on amorphous ice at 100 K was monitored directly by using resonance-enhanced multiphoton ionization. The translational energy distribution of the OH product was represented by a Maxwell-Boltzmann energy distribution with the translational temperature of 3250 ± 250 K. The rotational temperature was estimated to be 175 ± 25 K. We have confirmed that the OH production should be attributed to the secondary photolysis of H₂O₂ produced on ice surface on the basis of the results of controlled photolysis experiments for H₂O₂ doped on ice surface.