Translational and internal states of hydrogen molecules produced from the ultraviolet photodissociation of amorphous solid methanol

Translationally and internally hot H₂ molecules are produced from the 157 nm photodissociation of amorphous solid methanol at 90 K by two distinct mechanisms: exothermic recombination of two H-atom photoproducts bound to the surface and unimolecular molecular elimination of H₂ from the photoexcited methanol. The vibrationally hot H2 (v=2-5) products are characterized by high translational and rotational temperatures. A third mechanism, the almost thermoneutral abstraction of a hydrogen atom from methanol parent molecule by the photolytically produced hydrogen atom, yields translationally and rotationally cold H₂ (v=0 and 1) products. Comparison with the results of the vacuum ultraviolet photolysis of water ice is discussed. Production of translationally hot and cold hydrogen atoms is also confirmed.