Spectroscopic studies of the jet-cooled nickel dimer

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Abstract
We report the first gas‐phase electronic spectrum of nickel dimer. Ni2 is produced by laser vaporization of metallic nickel in the throat of a supersonic nozzle. Using resonant two photon ionization, bands previously observed in inert matrices and attributed to Ni2 are conspicuous in their absence. Further to the red, an abrupt onset of complicated spectral structure indicates rapid predissociation above 16 680 cm−1. We argue that this represents the true dissociation limit, and places D0=2.068±0.01 eV. A congested pattern of spectral features from 6000 to 9000 Å confirms theoretical predictions of a large number of low‐lying electronic states in nickel dimer. Rotationally resolved bands near 8500 Å are indicative of a ΔΩ=+1 transition, with Ω″=4, Ω′=5. Rotational analysis of these bands yields a bond length of 2.200±0.007 Å for the ground state of Ni2, which must be of either 1Γg or 3Γu electronic symmetry species. Both the long bond length of 2.20 Å and the high value of Ω″ are in agreement with theoretical predictions, and confirm that no substantial 3d participation contributes to the chemical bonding of Ni2.

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