A photoabsorption, photodissociation and photoelectron spectroscopy study of C2H4 and C2D4

Abstract The absolute photoabsorption, photoionisation and photodissociation cross-sections and the photoionisation quantum efficiency of benzene and hexadeuterobenzene have been measured from the ionisation threshold to 350 A using a double ion chamber and monochromated synchrotron radiation. The HeI excited photoelectron spectrum of C 6 D 6 has been recorded and the vibrational structure exhibited in the X  2 E 1g , A  2 E 2g , E  2 B 1u and F  2 A 1g bands has been analysed with the aid of theoretical predictions and by analogy with the recently reported high-resolution photoelectron spectrum of C 6 H 6 . The photoabsorption spectrum displays extensive vibrational structure extending from the ionisation threshold to ∼730 A, and many of these absorption features have been arranged into Rydberg series. A detailed assignment of the vibrational progressions associated with some Rydberg states has been accomplished by making use of the corresponding photoelectron spectrum. A sum rule analysis has been carried out by combining the present absolute photoabsorption measurements with similar data covering the remaining wavelength regions.