A study of the CF radical with PE and CIS spectroscopy: investigation of Rydberg states above the first ionization threshold

Abstract

The CF radical has been studied with photoelectron (PE) and constant-ionic-state (CIS) spectroscopy using synchrotron radiation. By scanning the photon energy in the region between the first and second ionization onsets, while monitoring the intensity of selected vibrational components in the first photoelectron band, excitations to Rydberg states, which are part of a series which converge to the second ionization limit, were revealed. By comparing PE spectra recorded at selected resonance positions with calculated Franck–Condon PE vibrational envelopes to establish the excited state vibrational numbering, fitting the observed resonance positions to Rydberg series, and comparing the results obtained with results from a preceding paper on the isoelectronic molecule NO (1), the structure obtained could be assigned to excitation to np Rydberg states with a CF⁺(a³Π) core. The Rydberg series fits led to an improved adiabatic ionization energy (AIE) from CF(X²Π) to the CF⁺(a³Π) state of (13.942 ± 0.003) eV.