Thorium Fluorides ThF, ThF2, ThF3, ThF4, ThF3(F2), and ThF5- Characterized by Infrared Spectra in Solid Argon and Electronic Structure and Vibrational Frequency Calculations

Reactions of laser-ablated Th atoms with F-2 produce ThF4 as the major product based on agreement with matrix spectra recorded of the vapor from the solid at 800-850 degrees C. Weaker higher-frequency bands at (567.2, 564.8), (575.9, 575.1), and (531.0, 528.4) cm(-1) in argon are assigned to ThF, ThF2 and ThF3, ThF3(F-2) on the basis of their chemical behavior upon increasing reagent concentrations, annealing, and irradiation, the use of NF3, OF2, and HF as F-atom sources, and a comparison with frequencies calculated at the DFT/B3LYP and CCSD(T) levels with a large segmented 4 ECP basis set on Th and the aug-cc-pVTZ basis set on F. An additional broader band at 460 cm(-1) is assigned to the ThF5- anion. The trigonal-bipyramidal ThF5- anion (calculated electron detachment energy of 7.17 eV) increases at the expense of ThF3(F-2) and F-3(-) on full mercury arc irradiation. [ThF3+][F-2(-)] is shown by calculations to be an ionic complex with a side-bound F-2(-) subunit. This paper reports the first evidence for novel pentacoordinated thorium species including the unique [ThF3+][F-2(-)] ionic radical-ion pair molecule and its electron-capture product, the very stable ThF5- anion.