A photoabsorption, photodissociation and photoelectron spectroscopy study of C2H4 and C2D4 Original Research Article

The absolute photoabsorption, photoionisation and photodissociation cross sections and the photoionisation quantum efficiency of ethylene and deuterated ethylene have been measured from the ionisation threshold to 500 Å using a double ion chamber and monochromated synchrotron radiation. High resolution photoelectron spectra of the same molecules have been recorded using HeI and HeII radiation, and detailed analyses have been made of the vibrational structure exhibited in the X2B3u, A2B3g, B2Ag, C2B2u and D2B1u photoelectron bands. In the inner valence binding energy region the HeII excited spectrum shows several satellite features which are due to configuration interaction effects. The photoabsorption spectra display extensive vibrational structure extending from the ionisation threshold to approximately 630 Å. With the aid of the high resolution photoelectron spectra, many of these absorption features have been arranged into vibrational progressions associated with Rydberg states. Tentative assignments for some of these states have been proposed based upon an assessment of terms values and quantum defects. A sum rule analysis has been carried out by combining the present absolute photoabsorption measurements with similar data covering the remaining wavelength regions.