A STUDY OF VMn AND $VMn^{-}$ BY NEGATIVE ION PHOTOELECTRON SPECTROSCOPY

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1997

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Ohio State University

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We report the 476-514 nm negative ion photoelectron spectra of VMn, a mixed early-late transition metal dimer which is isoelectronic with Cr2, The VMn anions were prepared in a flowing afterglow ion-molecule reactor through the addition of Mu2(CO)10 vapor downstream of a vanadium cathode discharge source. The spectrum is dominated by two intense transitions to the ground state and to one excited electronic state of neutral VMn, whose electron affinity is measured to be $0.524 \pm 0.005 $eV. Its ground state vibrational frequency is 570±20cm−1 vibrational spacings observed up to v=6 do not fit a Morse potential. An excited state observed at 14140±30cm−1 shows a much higher frequency of 680±20cm−1, and hot bands reveal a reduced frequency of 500±20cm−1 in the VMn anion. The similarities of these results to those previously obtained1 for Cr2 suggest that VMn also has a nominally hextuply bonded 1Σg(3dσg)2(3dπu)4(3dδg)4(4sσg)2 ground state, with the extra electron in the 2Σu+ anion occupying an sp hybridized σu orbital. Similarly, the observed VMn excited state is assigned as a (4sσg)1(spσu+)13Σu+ state whose increased vibrational frequency reflect a reduced 4s electron density in the dd bonding region. Additional weaker transitions observed at lower binding energies display a more complex pattern than those observed for Cr2 and are likely due, at least in part, to d electron detachment transitions to lower-lying excited states in VMn. Hot band intensities observed in spectra obtained at different ion source temperatures indicate a surprising lack of vibrational thermal equilibration of the anions.

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Author Institution: Department of Chemistry, University of Minnesota

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