REACTIONS OF PHOTOGENERATED FLUORINE-ATOMS WITH DOPANT MOLECULES IN SOLID ARGON .2. REACTION OF CH4 MOLECULES WITH FLUORINE-ATOMS DIFFUSINGIN SOLID ARGON AT 20-30 K

The products of reactions of dopant CH4 molecules with F atoms diffusi ng in solid argon at 20-30 K were identified by ESR and FTIR spectrosc opy. The F atoms stabilized in the matrix were generated by UV photoly sis of Ar-CH4(CD4)-F (1000 : 1 : 1) samples at 13 K. Subsequent heatin g above 20 K results in thawing off diffusion of the F atoms and forma tion of products of their reaction with CH4: radical-molecular complex es (CH3)-C-.-HF ((CD3)-C-.-DF) and radicals (CH3)-C-.((CD3)-C-.). The ESR spectra of the radicals are similar to chose observed for matrix-i solated (CH3)-C-.((CD3)-C-.). The (CH3)-C-.-HF complexes are character ized by the IR band of HF stretching vibration at 3764 cm(-1). Two add itional splittings on the H (a(H') = 2 G) and F (a(F) = 16 G) nuclei o f the HF molecule appear in the ESR spectrum of the complex. The latte r splitting is retained in the (CD3)-C-.-DF complex, where a(D') < 0.3 G. The rate constant of the reaction CH4 + F --> (CH3)-C-. + HF is eq ual to similar to 10(-25) cm(3) s(-1) at 20 K. Its activation energy ( 1.7+/-0.2 kcal mol(-1)) is similar to 0.5 kcal mol(-1) greater than th at in the gas phase. The collinear C-3v-configuration of the (CH3)-C-. -HF complex, which is similar to the configuration of the reagents in the transition state of the reaction considered, was established by th e comparison of the experimental constants of hyperfine coupling with the results of the quantum-chemical calculation.