MULTIPHOTON IONIZATION 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

The multiphoton ionisation spectra of ethyl iodide and its perdeuteria ted analogue in the region of the first Rydberg transitions are report ed and analysed. The observed vibronic structure has been completely a ccounted for by a small set of vibrational modes involving atoms adjac ent to the iodine atom. The origins identified are more numerous than can be explained by a direct comparison with the spectra and electroni c s`tructure of methyl iodide and it has been shown that states degene rate in the C-3v symmetry of methyl iodide are split by the C-s symmet ry molecular field of ethyl iodide. It has also been shown that there is a reordering of the energies of related states between methyl and e thyl iodide and an explanation in terms of different extents of 6s/6p Rydberg state mixing has been proposed. The energies of states determi ned are compared with those reported for HI and CH(3)l and the spectra are compared with spectra of higher alkyl iodides.