Anion photoelectron spectroscopy and chemical bonding of ThO2− and ThO3−

We conducted a study of electronic structures and chemical bonding of gaseous ThO2− and ThO3− using velocity-map imaging and ab initio calculations. The electron affinity of neutral ThO2 molecule is reported for the first time with the value of 1.21(5) eV. We obtained a vibrationally resolved photoelectron spectroscopy of ThO2− and observed the symmetric stretching frequency of 824(40) cm−1 for neutral molecules. One hot band transition is observed in the spectrum of ThO2−, which allows the measurement of symmetric stretching mode for ThO2−. The ground state of ThO2− is 2A1 with C2v symmetry: the detachment of an electron from the singly occupied molecular orbital (SOMO) results in the ground state of ThO2. Kohn-Sham molecular orbital analyses reveal an σ and two weak π bonds for Th–O multiple bonds in ThO2. Global minimum search methodology combined with quantum chemical calculations are used to find the minima of ThO3 and ThO3−, and the adiabatic detachment energy of ThO3− is calculated to be 3.26 eV at the coupled cluster with singles and doubles plus perturbative triples level. Our theoretical calculations suggest that the ground state of ThO3 is 1A′ with a symmetry of Cs, while the most stable ThO3− is 2A1 with C2v symmetry; thus, the transition from ThO3− to ThO3 undergoes a significant geometry reorganization. Molecular orbital analyses suggest that the SOMO of ThO3− is mainly participated by O 2p and O to Th back donation was found in HOMO-2 molecular orbital. This investigation will shed some light on the understanding of covalent bonding in Th-contained molecules.