V, Nb, and Ta hydride molecules in deuterium and rare-gas matrices: Infrared and electron spin resonance spectra

The VH2 molecule was found to have S=3/2 and a 4Σ ground state with a zero-field splitting parameter ‖D‖=0.315 cm−1. 51V (I=7/2) hyperfine splitting was observed in the ESR spectra, but the hydrogen hyperfine was unresolved. The narrowest lines were observed for VD2 in solid deuterium at ∼2 K. Efforts to observe VH4 via ESR were not successful presumably because it could not be prepared in a high enough concentration. The infrared spectra of NbH2 molecules and their deuterated isotopomers were observed in solid deuterium and rare-gas matrices. NbH2 was found to be bent at 130°, in accord with theoretical calculations. NbH2 was not observed in ESR spectra although it presumably has a 4B1 ground state; this is attributed to a large (≳4 cm−1) negative D value. NbH4 was observed via ESR as a tetragonally distorted (D2d) tetrahedral molecule in its 2B1 lowest state resulting from a static Jahn–Teller effect. 93Nb (I=9/2) and also H hyperfine splittings were observed. A corresponding TaH4 spectrum was attributed to a similarly distorted tetrahedral S=1/2 molecule.