MSX-ALPHA STUDY OF ABSORPTION-SPECTRA OF FREE-RADICALS - CHARACTERIZATION OF RYDBERG AND VALENCE TRANSITIONS IN ALKYL DERIVATIVES OF GROUP-14 CENTERED RADICALS

Ionization potentials, electronic transition energies, and oscillator strengths were computed by the MSXa method for methyl, ethyl, isopropyl, tert-butyl, and X3M· radicals (M = Si, Ge, Sn; X = H, CH3). The best procedure, within the MSXa framework, for assigning optical absorption spectra in radicals was established. In alkyl and H3M· radicals, the transition energies are in very good agreement with experiment and available ab initio Cl calculations. The optical spectra of alkyl derivatives of heteroatom-centered radicals are assigned for the first time. The low-lying transitions are predominantly Rydberg in character and are red shifted as the degree of alkyl substitution increases or the electronegativity of the central atom M decreases in accordance with the trend of the vertical ionization potentials. In heteroatom-centered radicals, the first valence from the M-C bond to SOMO is strongly red shifted and occurs in the range of the lowest Rydberg transitions. © 1993, IEEE. All rights reserved. © 1990, American Chemical Society. All rights reserved.