Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC<sup>+/0/–</sup>
Gabriel F. de Melo, Monica Vasiliu, Gaoxiang Liu, Sandra M. Ciborowski, Zhaoguo Zhu, Moritz Blankenhorn, Rachel M. Harris, Chalynette Martinez‐Martinez, Maria Dipalo, Kirk A. Peterson, Kit H. Bowen, David A. Dixon
Abstract
A combination of high-level ab initio calculations and anion photoelectron detachment (PD) measurements is reported for the UC, UC–, and UC+ molecules. To better compare the theoretical values with the experimental photoelectron spectrum (PES), a value of 1.493 eV for the adiabatic electron affinity (AEA) of UC was calculated at the Feller–Peterson–Dixon (FPD) level. The lowest vertical detachment energy (VDE) is predicted to be 1.500 eV compared to the experimental value of 1.487 ± 0.035 eV. A shoulder to lower energy in the experimental PD spectrum with the 355 nm laser can be assigned to a combination of low-lying excited states of UC– and excited vibrational states. The VDEs calculated for the low-lying excited electronic states of UC at the SO-CASPT2 level are consistent with the observed additional electron binding energies at 1.990, 2.112, 2.316, and 3.760 eV. Potential energy curves for the Ω states and the associated spectroscopic properties are also reported. Compared to UN and UN+, the bond dissociation energy (BDE) of UC (411.3 kJ/mol) is predicted to be considerably lower. The natural bond orbitals (NBO) calculations show that the UC0/+/– molecules have a bond order of 2.5 with their ground-state configuration arising from changes in the oxidation state of the U atom in terms of the 7s orbital occupation: UC (5f27s1), UC– (5f27s2), and UC+ (5f27s0). The behavior of the UN and UC sequence of molecules and anions differs from the corresponding sequences for UO and UF.