Flowing Afterglow Negative Ion Photoelectron Spectroscopy of Dirhenium: Evidence for Multiple Bonding in Re₂ and Re₂^-

Although there is now an extensive spectroscopic literature concerning homonuclear diatomics of first-row transition metals, relatively little is known about dimers of the second and third transition series. Theoretical calculations for third-row systems predict more comparable (n + 1 )s and nd orbital sizes and energies than for their lighter congeners, due primarily to relativistic effects. This trend is expected to yield enhanced d-d bonding in third-row dimers, a prediction consistent with reported³ mass spectrometric dissociation energies. Spectroscopic confirmation of these predictions has not yet been possible, due to the nearly⁴ total lack of data for dimers of open d-shell third-row metal atoms.