Electronic structure of vanadium tetramer ion studied by optical absorption spectroscopy

The optical absorption spectrum of a vanadium tetramer ion, V-4(+), was Obt ained by measuring a photodissociation efficiency of an ion complex, V-4(+) Ar, as a function of the photon energy of the laser pulse used for the pho todissociation. The optical absorption spectrum thus obtained was simulated by a density functional calculation to search for the most probable geomet ric structure which reproduces the measured spectrum. The analysis showed t hat V-4(+) is most likely to have a ''distorted'' tetrahedral structure wit h C-2 upsilon symmetry. The ground electronic state of V-4(+) was found to be a low spin state, (2)A(1). The relatively broad spectral profile is expl ained in terms of the distortion related to a low-energy vibration. Geometr y optimization;of the Amsterdam density functional (ADF) calculation also p redicts C-2 upsilon Symmetry for the structure of V-4(+). (C) 1998 American Institute of Physics. [S0021-9606(98)00546-7].