Ultraviolet (UV) irradiation of HI-doped xenon matrix dissociates the precursor and leads to the formation and trapping of neutral atoms. After UV photolysis, annealing of the matrix mobilizes the hydrogen atoms 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 2950-3800 cm(-1) and quantitatively regenerated thermally. The formation of HXeI from neutral atoms is proved by the quantitative correlation between neutral iodine atoms and HXeI molecules in selective IR photodissociation and thermal regeneration experiments. Kinetic measurements show that the formation of HXeI from atoms is prevented by a potential barrier, which is estimated to be 700 cm(-1) in magnitude. The potential barrier is proposed to originate from the avoided crossing between neutral H+Xe+I and ionic (HXe)(+)+I- singlet surfaces. The dissociation energy D-0 of HXeI with respect to the top of the potential barrier is estimated 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 measured by irradiating the sample with tunable IR source and monitoring the changes in the fundamental region. The formation mechanism from neutral atoms is believed to be valid for other similar rare-gas compounds. (C) 1997 American Institute of Physics. [S0021-9606(97)01844-8].