Resonance-enhanced multiphoton ionisation spectroscopy of thiirane

Abstract

We present a new and more extensive interpretation of the vertical electronic spectrum of the thiirane molecule based on (i) analysis of observed two- and three-photon resonance enhancements in the wavelength-resolved multiphoton ionisation spectrum of jet-cooled thiirane and (ii) measurements of the kinetic energies of the photoelectrons accompanying the multiphoton ionisation process. Six Rydberg series are identified, including the four series identified in previous one-photon vacuum ultraviolet absorption studies of this molecule. Series assignments are offered based on the measured quantum defects, their relative two- and three-photon transition strengths and the dependence (if any) of the two-photon transition intensities upon changing from linearly to circularly polarised photoexcitation. Our analysis suggests that, as in H₂S, many of the Rydberg orbitals have hybrid / character; it also points to the need for some revision of all previous interpretations of the electronic spectrum of the thiirane molecule.