The metal concentration and matrix conditions which favor the dimerization of vanadium atoms to divanadium molecules are quantitatively assessed using optical spectroscopy. A simple kinetic theory is presented which enables small metal clusters to be identified in the presence of atomic species. This approach makes use of the fact that a metal atom being deposited is capable of diffusing either on the matrix surface or within a narrow region (the reaction zone) near the matrix surface before its kinetic energy is dissipated sufficiently to immobilize it. The surface diffusion pathway is found to predominate over the statistical generation of dimers. The kinetic result, which suggests that V2 is formed on the matrix surface rather than in the gas phase, is also borne out by the intriguing observation that for a given metal deposition rate the dimer-to-monomer ratio decreases as one increases the atomic weight of the noble gas used to isolate them, with Ar giving the most V2 and Xe the least. Careful concentration experiments in Ar, Kr, and Xe matrices permit the uv–visible transitions of V2 to be identified and the extinction coefficient ratio epsilonV/epsilonV2 to be determined. A qualitative molecular orbital description of V2 is presented in the light of iterative extended Hückel calculations. These computations suggest that high spin divanadium has a strong metal–metal bond which is mainly 4s in character with only small contributions from the degenerate dxz,yz pi-bonding set. Visible absorptions observed in the 600–450 nm region are tentatively assigned to electronic transitions localized mainly between the V–V sigma-bond and the d-orbital manifold. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.