Spectroscopic investigations of ThF and ThF +

Abstract

The electronic spectra of ThF and ThF + have been examined using laser induced fluorescence and resonant two-photon ionization techniques. The results from high-level ab initio calculations have been used to guide the assignment of these data. Spectra for ThF show that the molecule has an X 232 ground state. The upper spin-orbit component, X 252 was found at an energy of 2575(15)cm -1. The low-lying states of ThF + were probed using dispersed fluorescence and pulsed field ionization - zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy. Vibronic progressions belonging to four electronic states were identified. The lowest energy states were clearly 1∑ + and 31. Although the energy ordering could not be rigorously determined, the evidence favors assignment of 1∑ + as the ground state. The 31 state, of interest for investigation of the electron electric dipole moment, is just 315.0(5)cm -1 above the ground state. The PFI-ZEKE measurements for ThF yielded an ionization energy of 51 581(3)cm -1. Molecular constants show that the vibrational constant increases and the bond length shortens on ionization. This is consistent with removal of a non-bonding Th-centered 6d or 7s electron. Laser excitation of ThF + was used to probe electronically excited states in the range of 19 000-21 500cm -1. © 2012 American Institute of Physics.