“…Obtaining atomic properties of the actinides from direct calculations is also difficult, but a way to probe the electronic structure of an actinide is to examine the An−H interaction. Our prior calculations at the SO-CASPT2 level on the early actinide monohydrides, AcH (7s 2 ), 2 ThH (6d 1 7s 2 ), 3,4 PaH (5f 2 7s 2 ), 2 and UH (5f 3 7s 2 ), 5 showed that there are 10, 26, 63, and 51 accessible states within 1.6 eV for the Ac, Th, Pa, and U hydrides, respectively, as the introduction of valence 5f electrons increases the number of excited states but not in a simple fashion. At the Feller−Peterson−Dixon (FPD) level, 6−9 based on combining CCSD(T) calculations extrapolated to the complete basis set limit, adiabatic electron affinities (AEA) were predicted to increase from AcH (0.42 eV) to ThH (0.82 eV) and then to decrease for PaH (0.78 eV) to UH (0.46 eV).…”