Ionic and Rydberg states of CF3I studied by high resolution photoelectron (ZEKE-PFI) and resonance-enhanced multiphoton ionisation spectroscopy
Abstract
Ionic and Rydberg states of CF3I have been studied using both zero kinetic energy pulsed-field ionisation (ZEKE-PFI) photoelectron and resonance-enhanced multiphoton ionisation (REMPI) spectroscopy. The ground state of the ion (2E3/2) was characterised using coherent two-photon (one-colour) ZEKE-PFI spectroscopy and extended progressions in the symmetric vibrational modes, similar to those observed in the conventional He(I) photoelectron spectrum, were observed at high resolution. The [2E3/2]6p Rydberg states were studied using two- and three-photon REMPI spectroscopy with linearly and circularly polarised light. This resulted in the assignment of at least three states with distinct Ω values (2, 1 and 0) with the Ω=2 components being the most intense. The strongest members of the [2E3/2]6p;2 system were used as resonant intermediates in two-colour (2+1′) ZEKE-PFI experiments which allowed the unambiguous assignment of the majority of the vibrational structure of the intermediate states. The adiabatic ionisation energy of CF3I was determined as 83652±2 cm-1. The vibrational structure observed for one of the Ω=2 components of the [2E3/2]6p cluster in CF3I differs considerably from that observed for the lower lying 6s states and the analogous 6p states of CH3I. In particular, ν3 (the carbon–iodine stretch) shows a vibrational frequency substantially reduced from that of the neutral and ionic ground states. It is concluded that at least one of the [2E3/2]6p states of CF3I is distorted, possibly through an interaction with an ion-pair state.