Laser spectroscopy and ab initio studies of metal-containing free radicals

• Main Author: Greetham, Gregory Michael
• Published: University of Leicester 2000
• Subjects: 543
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.696798

This work describes the use of laser spectroscopy and ab initio calculations in the investigation of several new electronic transitions in metal-containing free radicals. These free radicals were prepared in a supersonic jet by laser ablation of solid metal samples in the presence of appropriate precursor molecules. The first spectroscopic observation of the Ga-N2 van der Waals cluster is reported. Laser-induced fluorescence (LIF) spectra have revealed two strong band systems in the near ultraviolet correlating with transitions of atomic gallium. Long vibrational progressions due to activity in the van der Waals stretching mode were observed in both systems. Supporting ab initio calculations on the group 13 atom-nitrogen molecule clusters confirm that these clusters are linear in their ground electronic states. New electronic transitions of the CaNC and SrNC free radicals have been identified in the near ultraviolet. These include the D˜ -- X˜ transition of CaNC and the D˜ -- X˜ and E˜ -- X˜ transitions of SrNC. The first jet-cooled investigation of the SrNC C˜ -- X˜ transition was also performed. All the spectra showed complex vibrational structure which has been attributed to activity in the bending mode. This has been used to infer that a non-linear equilibrium geometry is adopted in the upper electronic states, in contrast to the linear ground electronic states. The first observation of the lowest 2Delta state of a strontium-containing free radical is reported, that of SrCCH. This new excited electronic state is accessed by the orbitally-forbidden B˜' 2Delta-X˜ 2Sigma + transition. Spin-orbit and vibrational structure have been seen in spectra of SrCCH and SrCCD and confirmed the assignment. Finally, observation of a new transition in an unidentified gallium-containing molecule is reported. Two progressions corresponding to two different vibrational modes of the molecule are seen in the spectrum. Potential spectral carriers, including Gax clusters and other gallium-containing molecules formed by reaction with impurities, are discussed in an attempt to explain the observed spectrum.