THE MECHANISM OF FORMATION AND INFRARED-INDUCED DECOMPOSITION OF HXEIIN SOLID XE

Ultraviolet (UV) irradiation of HI-doped xenon matrix dissociates the precursor and leads to the formation and trapping of neutral atoms. Af ter UV photolysis, annealing of the matrix mobilizes the hydrogen atom s at about 38 K. The mobilized hydrogen atoms react with I/Xe centers forming HXeI molecules in a diffusion controlled reaction. The formed molecules can be photolyzed with infrared (IR) irradiation at 2950-380 0 cm(-1) and quantitatively regenerated thermally. The formation of HX eI from neutral atoms is proved by the quantitative correlation betwee n neutral iodine atoms and HXeI molecules in selective IR photodissoci ation and thermal regeneration experiments. Kinetic measurements show that the formation of HXeI from atoms is prevented by a potential barr ier, which is estimated to be 700 cm(-1) in magnitude. The potential b arrier is proposed to originate from the avoided crossing between neut ral H+Xe+I and ionic (HXe)(+)+I- singlet surfaces. The dissociation en ergy D-0 of HXeI with respect to the top of the potential barrier is e stimated to be 2950 cm(-1) and D-e about 4070 cm(-1) in solid Xe. The weak IR photodissociation profile of HXeI around 3000 cm(-1) is measur ed by irradiating the sample with tunable IR source and monitoring the changes in the fundamental region. The formation mechanism from neutr al atoms is believed to be valid for other similar rare-gas compounds. (C) 1997 American Institute of Physics. [S0021-9606(97)01844-8].