A PHOTOABSORPTION, PHOTODISSOCIATION AND PHOTOELECTRON-SPECTROSCOPY STUDY OF C2H4 AND C2D4

The absolute photoabsorption, photoionisation and photodissociation cr oss sections and the photoionisation quantum efficiency of ethylene an d deuterated ethylene have been measured from the ionisation threshold to 500 Angstrom using a double ion chamber and monochromated synchrot ron radiation. High resolution photoelectron spectra of the same molec ules have been recorded using HeI and HeII, radiation, and detailed an alyses have been made of the vibrational structure exhibited in the (X B3u)-B-2, A(2)B(3g), B(2)A(g), (CB2u)-B-2 and (DB1u)-B-2 photoelectron bands. In the inner valence binding energy region the HeII excited sp ectrum shows several satellite features which are due to configuration interaction effects. The photoabsorption spectra display extensive vi brational structure extending from the ionisation threshold to approxi mately 630 Angstrom. With the aid of the high resolution photoelectron spectra, many of these absorption features have been arranged into vi brational progressions associated with Rydberg states, Tentative assig nments for some of these states have been proposed based upon an asses sment of term values and quantum defects. A sum rule analysis has been carried out by combining the present absolute photoabsorption measure ments with similar data covering the remaining wavelength regions.