The He1 vacuum ultraviolet photoelectron spectrum of the methyl radical produced by pyrolysis of azomethane has been investigated. Three ionization potentials, corresponding to the for!m!ion of the ' A ; , 3E' and 'E' ionic states, have been observed with vertical ionization potentials of 9.54, 14.76 and 16.10eV respectively. The observed band positions have been interpreted with tb: aid of both ab initio and semiempirical molecular orbital calculations.The band associated with the first ionization potential is the only one for which \ibrational structure could be rcsolved. This has been investigated in both CH3 and CD3 using He1 and Ye1 radiation. From the Franck-Condon envelope of this band and the observed shifts on deatcration, it is concluded that the methyl radical is essentially planar in its ground electronic state. The hctors which control the values of the out-of-plane deformatim frequencies in the ground state of CH, and CH; are discussed in detail. Jahn-Teller splitting has been detected in the band arsminted with the sxond ionization potential of CH,.

The vacuum ultraviolet photoelectron spectrum of the t-butyl radical produced by pyrolysis of 2,2' azoisobutane has been investigated. The band associated with the first ionization potential is the only one for which vibrational structure could be resolved and this has been analysed in terms of ionization of a vibrationally excited t-butyl molecule. From the observed Franck-Condon envelope of this band, it is concluded that the t-butyl radical has a pyramidal C3v geometry in its ground electronic state and the barrier to inversion is estimated to be (900±100) cm-1 with an out-of-plane distance of the central carbon atom of (0.30±0.05) Å. The first vertical and adiabatic ionization potentials of the t-butyl radical are estimated to be (6.90±0.01) eV and (6.58±0.01) eV respectively. The higher ionization potential region is interpreted with the aid of semiempirical molecular orbital calculations.