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.