Electronic spectroscopic studies of diatomic molecules containing transition and actinide metals

Abstract

The optical spectrum of various gas-phase diatomic molecules containing transition and actinide metals were collected and studied using the resonant two-photon ionization spectroscopic method. The molecules of interest reported here are uranium nitride (UN), chromium tungsten (CrW), and six iron- and nickel-containing molecules: FeX and NiX (X = C, S, Se). The optical transitions of UN were investigated from 19 200 to 23 900 cm -1, resulting in a very large number of bands being observed. The rotationalstructure of seven of these bands were collected and analyzed, all originating from the same ground electronic state. It was determined that the ground state of UN has Ω = 3.5, with a bond length, r0, of 1.7650(12) A. Additionally, comparisons were made to isovalent species. The vibronically resolved spectrum of CrW was recorded over the region 21 100 to 23 400 cm -1, which also exhibited a very large number of bands.Seventeen of these bands were rotationally resolved and analyzed, all found to originate from the ground 1Σ+ state of the molecule and terminating on states with ?? = 0. Across the isotopologues studied, the average bond length of the ground state was determined to be 1.8814(4) A. In addition to this information, the bond dissociation energy, D0, of CrW was observed to be 2.867(1) eV and a multiple bonding radius was able to be calculated to be 1.037 A. The bond dissociation energies of FeC, NiC, FeS, NiS, FeSe, and NiSe have been measured by the observation of a predissociation threshold in the optical spectra of these species. From the observed thresholds, dissociation energies have been measured as D0(FeC) = 3.961(19), D0(NiC) = 4.167(3), D0(FeS) = 3.240(3), D0(NiS) = 3.651(3), D0(FeSe) = 2.739(3), and D0(NiSe) = 3.218(3) eV. Through the use of thermochemical cycles, these values have been combined with other well-known quantities to improve the accuracy of other quantities. The periodic trends noted are discussed in terms of a molecular orbital diagram for these species. Finally, these results have also been used to calculate 0 K enthalpies of formation of the MX molecules.