An INDO study of the hyperfine coupling constants and equilibrium geometries of some tetra-atomic radicals

Abstract

Equilibrium geometries and isotropic hyperfine coupling constants have been estimated for the series of radicals CHnF3_n, CHnCla-n, CClnFa_n and S1HnF~-n using the INDO method. The theoretical hyperfine splittings agree well with experimental values including the unusually large proton splittings of 34"6 G and 89"9 G recently reported for SiH2F and SiHF~.

Twofold coordinated Si and Ge atoms and “hydrogen” paramagnetic centers in amorphous SiO2 and GeO2

“…ESR parameters of fluorideand oxygen-containing radicals of a similar structure (No. 1,3,7,8 in Table 1) are similar. From this we conclude that the (A) center has a geometry close to the &F2H radical, that is the 0-Si-0 angle is about 104" and for 0-Si-H it is about 110". '…”

“…'y -type centers depends on the degree of deviation of the radical geometry from a planar one [ 5 ] . The experimental data [6, 71 and the results of quantum-chemical calculations by the INDO method [8] of ESR parameters for radicals SiH,, SiH,F, SiHF,, SiF, are listed in Table 1. The isotropic proton splitting constant increases in the series from SiH, to SiHF, owing to the change of center geometry (SiH,: H-Si-H = 111"; SiH,F: H-Si-H = 114", F-Si-H = 105.8"; SiHF,: H-Si-F = = 109.6", F-Si-F = 104"; SiF3: F-Si-F = 106.8' [S]).…”

SILICON-29 HYPERFINE SPLITTING OF THE SiH3 RADICAL

“…[10][11][12] It is very interesting that the isotropic 29Si-hf splitting of 182 G of the SiH3 radical is equal, within experimental errors, to those of the methyl-substituted silyl radicals ( McSiH2, Me 2SiH, and Me3Si) obtained in both fluid solutions') and solid matrices. This implies that the mean bond angles at the silicon atom of these radicals are, to a first approximation, unaffected by the successive methyl-substitution.…”