The photoelectron-imaging spectroscopic study and chemical bonding analysis of VO(2)(−), NbO(2)(−) and TaO(2)(−)

The transition-metal di-oxides, namely VO(2)(−), NbO(2)(−) and TaO(2)(−) have been studied using photoelectron velocity map imaging (PE-VMI) in combination with theoretical calculations. The adiabatic electron affinities of VO(2)(−), NbO(2)(−) and TaO(2)(−) are confirmed to be 2.029(8), 1.901(10) and 2.415(8) eV, respectively. By combining Franck–Condon (FC) simulation with theoretical calculations, the vibrational feature related to Nb–O and Ta–O stretching modes for the ground state has been unveiled. The photoelectron angular distribution (PAD) for VO(2)(−), NbO(2)(−) and TaO(2)(−) is correlated to the photo-detachment of the highest occupied molecular orbitals (HOMOs), which primarily gets involved in s- and d-orbitals of the V, Nb and Ta atoms. A variety of theoretical calculations have been used to analyze the chemical bonding features of VO(2)(−1/0), NbO(2)(−1/0) and TaO(2)(−1/0), which show that the strong M–O (M = V, Nb and Ta) bond is mainly characterized as ionicity.