ESR of Free Radicals Trapped in Inert Matrices at Low Temperature: CH3, SiH3, GeH3, and SnH3

The free radicals CH3, SiH3, GeH3, and SnH3 have been produced in a krypton matrix at 4.2°K by γ irradiation of the matrix containing dilute concentrations of CH4, SiH4, GeH4, and SnH4. The electron spin resonances indicate free or restricted rotation for all the radicals in the matrix. Observed anisotropies in g show that SiH3, GeH3, and SnH3execute restricted rotation about an axis perpendicular to the symmetry axis. From the observed values for the rotating radicals, the axially symmetric principal g values for the static radicals are derived as follows: for SiH3, g∥ = 2.003, g⊥ = 2.007; for GeH3, g∥ = 2.003, g⊥ = 2.017; for SnH3, g∥ = 2.003, g⊥ = 2.025. Hyperfine structure caused by 29Si is observed for SiH3 with isotropic coupling constant Af = 266 G and anisotropic coupling Aμ = 24 G. These couplings reveal 22% scharacter in the orbital of the unpaired electron, which indicates that the radical is nonplanar with bond angles of 110.6°. Probably GeH3 and SnH3 are also nonplanar. The magnitudes of the isotropic proton couplings are: 23, 8.1, 15, and 26 G, respectively, for CH3, SiH3, GeH3, and SnH3. The coupling of SiH3 is probably negative like that for CH3, but that of GeH3 and of SnH3 may be positive.