Xenon trifluoride radicals were generated by the solid-state chemical reaction of mobile fluorine atoms with XeF2 molecules isolated in a solid argon matrix. On the basis of spectroscopic and kinetic FTIR measurements and performed quantum chemical calculations, two infrared absorption bands at 568 (strong) and 523 (very weak) cm(-1) have been assigned to asymmetric and symmetric Xe-F stretching vibrational modes of radical (XeF3)-Xe-center dot, respectively. Chemical reaction of fluorine atom with XeF2 in a solid argon cage obeys specific kinetic behavior indicating the formation of a long-lived intermediate complex under the condition that the diffusing fluorine atom is attached to isolated XeF2 at temperatures 20 K < T < 27 K. Subsequent thermally activated conversion in the complex is the main source of novel xenon-containing radical species (XeF3)-Xe-center dot. The rate constant and energy barrier are estimated for the reaction in an argon cage, [XeF2-F]->(K)(r) [XeF3], as K-r similar to 7 x 10(-5) c(-1) at 27 K and E approximate to 1.2 kcal/mol, respectively. Quantum chemistry calculations reveal that radical (XeF3)-Xe-center dot has a planar C-2 nu structure. DFT calculations show that formation of the third Xe-F bond in the (XeF3)-Xe-center dot radical is exothermic, and the binding energy of the third Xe-F bond is 8-20 kcal/mol.