Photoinduced reactions of methyl radical in solid parahydrogen

Photolysis of methyl iodide in solid parahydrogen (p-H-2) at about 5 K is studied with ultraviolet light at 253.7 and 184.9 nm. It is found that the light at 253.7 nm produces only methyl radical, whereas the light at 184.9 nm yields both methyl radical and methane. The mechanism of the formation of the photoproducts is elucidated by analyzing the temporal behavior of the observed vibrational absorption. It is concluded that methyl radical in the ground state does not react with p-H-2 molecules appreciably but that the radical in the electronic excited state of (B) over tilde ((2)A(1)'), accessible by reabsorption of 184.9 nm photons by the radical, decomposes to a singlet methylene CH2 (a) over tilde((1)A(1)) and a hydrogen atom (S-2) and that the singlet methylene reacts with a p-H-2 molecule to give methane. (C) 1998 American Institute of Physics. [S0021-9606(98)00139-1].