Photostimulated desorption of OH radicals from amorphous solid water: Evidence for the interaction of visible light with an OH-ice complex

Using a combination of photostimulated desorption and resonance-enhanced multiphoton ionization techniques, OH radicals photodesorbed from amorphous solid water at low temperatures are detected. It was found that the OH photodesorption can be caused by a one-photon process on the surface even at 532 nm, where both isolated OH and ${\mathrm{H}}_{2}\mathrm{O}$ are transparent. Quantum chemical calculations reveal that the electronic excitation of OH dramatically changes depending on the adsorption sites and the number of surrounding ${\mathrm{H}}_{2}\mathrm{O}$ molecules, and that OH having three hydrogen bonds with neighboring ${\mathrm{H}}_{2}\mathrm{O}$ molecules can absorb photons of around 532 nm, which supports the experimental findings.