A photoabsorption, photodissociation and photoelectron spectroscopy study of C₆H₆ and C₆D₆

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 Å using a double ion chamber and monochromated synchrotron radiation. The HeI excited photoelectron spectrum of C₆D₆ has been recorded and the vibrational structure exhibited in the X ²E_1g, A ²E_2g, E ²B_1u and F ²A_1g bands has been analysed with the aid of theoretical predictions and by analogy with the recently reported high-resolution photoelectron spectrum of C₆H₆. The photoabsorption spectrum displays extensive vibrational structure extending from the ionisation threshold to ~730 Å, 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.