Infrared spectroscopic study on photolysis of ethyl iodide in solid parahydrogen: Perdeuterated iodide system

Perdeuterated ethyl iodide in solid parahydrogen is photolyzed at 4.4 K to find the formation of all deuterated ethylene, ethane, and ethyl radical an d deuterium iodide. The temporal change in the intensity of the vibrational spectra upon UV irradiation reveals that the initial ethyl iodide exists i n both monomeric and dimeric units. The monomeric unit is subjected to the following competitive reactions: C2D5I + h nu --> .C2D5 + .I and C2D5I + h nu --> CD2=CD2 + DI The ethylene produced thereby is loosely complexed with the counterpart DI. The dimeric unit undergoes the following one-photonic parallel reactions I and II: (I) (C2D5I)(2) + h nu --> 2 .C2D5 + I-2 to be followed by a gradual disproportionation, 2 .C2D5 --> CD2=CD2 + C2D6, which proceeds by quantum tunneling of a D atom between the radicals in the expe rimental time scale. The possible recombination of the two radicals to buta ne is not observed at all. (II) (C2D5I)(2) + h nu --> CD2=CD2 + C2D6 + h, w hich is a direct molecular process to give the same products as (I). The et hylene produced by both (I) and (II) tends to form complexes with C2D6 and with I-2. Prolonged irradiation induces the following secondary photolysis of the three primary photoproducts: .C2D5 + h nu --> CD2=CD2 + .D, DI + h n u --> .D + .I, and I-2 + h nu --> 2 .I.