Multiphoton spectroscopy of Rydberg states of tetrachloroethylene

Abstract

Spectroscopic studies of two-photon resonant vibronic bands of the (π,np) and (π,nf) Rydberg series of jet-cooled C2Cl4 are reported. Polarization ratio measurements for each transition and comparisons of experimental and calculated chlorine isotope shifts permitted the unambiguous assignment of vibronic band structure. Ab initio self-consistent field calculations of the harmonic frequencies for the optimized ground state geometry of C2Cl4 were performed for each of the seven isotopic chlorine compositions to assist interpretation of the isotope shift measurements. The 4p-Rydberg bands are quite weak and strongly perturbed, suggestive of localized Rydberg–valence state configuration mixing. The nf-Rydberg series provides a measurement of the first ionization potential for C2Cl4 of 75 216±5 cm−1 in good agreement with previous measurements. Mass analysis of ion fragmentation patterns reveals a multiphoton ladder switching excitation mechanism.