Multiphoton ionisation spectroscopy of ethyl iodide and deuteriated ethyl iodide in the region of the 6s Rydberg transitions. Evidence of molecular field splitting of spin–orbit degenerate states

Abstract

The multiphoton ionisation spectra of ethyl iodide and its perdeuteriated analogue in the region of the first Rydberg transitions are reported and analysed. The observed vibronic structure has been completely accounted for by a small set of vibrational modes involving atoms adjacent to the iodine atom. The origins identified are more numerous than can be explained by a direct comparison with the spectra and electronic structure of methyl iodide and it has been shown that states degenerate in the C_3v symmetry of methyl iodide are split by the C_s symmetry molecular field of ethyl iodide. It has also been shown that there is a reordering of the energies of related states between methyl and ethyl iodide and an explanation in terms of different extents of 6s/6p Rydberg state mixing has been proposed. The energies of states determined are compared with those reported for HI and CH₃I and the spectra are compared with spectra of higher alkyl iodides.