BOND STRENGTHS OF TRANSITION-METAL DIMERS - TIV, V2, TICO, AND VNI

The abrupt onset of predissociation in a severely congested electronic spectrum has been used to measure the bond strengths of jet-cooled TiV, V2, TiCo, and VNi by resonant two-photon ionization spectroscopy. The measured values are D0(0)(TiV) = 2.068 +/- 0.001 eV, D0(0)(V2) = 2.753 +/- 0.001 eV, D0(0)(TiCo) = 2.401 +/- 0.001 eV, and D0(0)(VNi) = 2.100 +/- 0.001 eV. It is proposed that two criteria must be satisfied in order that bond strengths may be determined by this method: (1) the molecule must possess a sufficient density of electronic states near the lowest dissociation threshold, so that nonadiabatic couplings can readily induce predissociation, and (2) the lowest separated atom limit must generate repulsive potential energy curves, so that the potential curves are not nested and, as a result, poorly coupled. Finally, the bond strengths of TiV, V2, TiCo, VNi, Ni2, NiPt, and Pt2 are compared to the corresponding filled d-subshell analogues, and the magnitude of d-orbital contributions to the chemical bonding in these molecules is evaluated.