Electron Spin Resonance of Free Radicals Formed from Group-IV and Group-V Hydrides in Inert Matrices at Low Temperature
The electron-spin-resonance spectra of molecular free radicals formed from the group-IV and group-V hydrides at 4.2°K in the xenon matrix have been observed and compared with those observed in krypton and other matrices. From these spectra, certain properties of the free radicals and certain matrix effects have been derived. Molecular free radicals formed by γ irradiation of a matrix containing PH3 or AsH3 are PH2 and AsH2, respectively. From analysis of the hyperfine structure, the P-bonding orbitals of PH2 were found to have 20.6% 3s character in the Xe matrix, compared with 19% in the Kr matrix. Because of anisotropies in the coupling and in the g tensor the hyperfine structure of AsH2 could not be measured. In the Xe matrix the average g is 2.0050 for PH2, and 2.034 for AsH2. No spectra could be observed for SbH2, although evidence for dissociation of SbH2 was indicated by the strong H-atom lines observed for a γ-irradiated sample of SbH3 in the Xe matrix. Molecular free radicals formed by γ irradiation of the group-IV hydrides are CH3, SiH3, GeH3, and SnH3. The observed hyperfine structure caused by the isotopes 29Si, 73Ge, and 117,119Sn indicate that the radicals SiH3, GeH3, and SnH3 are not planar like CH3, but are pyramidal in structure. Noticeable difference in the isotropic coupling of 29Si for the Kr matrix, 240 G, and for the Xe matrix, 190 G, indicates strong interaction of the matrix with the SiH3 radicals.