The UV spectra of primary, secondary, and tertiary alkyl radicals

Gas phase absorption spectra have been measured for one primary, three secondary, and two tertiary alkyl radicals in the 195 to 370 nm wavelength range. Radicals were generated by Hg-photosensitized reactions and observed by modulation spectroscopy. The pattern of bands observed agrees well with ab initio predictions for the 3s, 3p, and 3d Rydberg transitions and can be reproduced by a Rydberg formula using experimental vertical ionization potentials and normal quantum defects. Oscillator strengths and condensed phase blue shifts are consistent with the Rydberg assignment. A similarity with the spectra of primary, secondary, and tertiary amines is noted.