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Title: Rotationally resolved state-to-state photoionization and photoelectron study of titanium carbide and its cation (TiC/TiC{sup +})

Titanium carbide and its cation (TiC/TiC{sup +}) have been investigated by the two-color visible (VIS)-ultraviolet (UV) resonance-enhanced photoionization and pulsed field ionization-photoelectron (PFI-PE) methods. Two visible excitation bands for neutral TiC are observed at 16 446 and 16 930 cm{sup −1}. Based on rotational analyses, these bands are assigned as the respective TiC({sup 3}Π{sub 1}) ← TiC(X{sup 3}Σ{sup +}) and TiC({sup 3}Σ{sup +}) ← TiC(X{sup 3}Σ{sup +}) transition bands. This assignment supports that the electronic configuration and term symmetry for the neutral TiC ground state are …7σ{sup 2}8σ{sup 1}9σ{sup 1}3π{sup 4} (X{sup 3}Σ{sup +}). The rotational constant and the corresponding bond distance of TiC(X{sup 3}Σ{sup +}; v″ = 0) are determined to be B{sub 0}″ = 0.6112(10) cm{sup −1} and r{sub 0}″ = 1.695(2) Å, respectively. The rotational analyses of the VIS-UV-PFI-PE spectra for the TiC{sup +}(X; v{sup +} = 0 and 1) vibrational bands show that the electronic configuration and term symmetry for the ionic TiC{sup +} ground state are …7σ{sup 2}8σ{sup 1}3π{sup 4} (X{sup 2}Σ{sup +}) with the v{sup +} = 0 → 1 vibrational spacing of 870.0(8) cm{sup −1} and the rotational constants of B{sub e}{sup +} = 0.6322(28) cm{sup −1}, and α{sub e}{sup +} = 0.0085(28) cm{sup −1}.more » The latter rotational constants yield the equilibrium bond distance of r{sub e}{sup +} = 1.667(4) Å for TiC{sup +}(X{sup 2}Σ{sup +}). The cleanly rotationally resolved VIS-UV-PFI-PE spectra have also provided a highly precise value of 53 200.2(8) cm{sup −1} [6.5960(1) eV] for the adiabatic ionization energy (IE) of TiC. This IE(TiC) value along with the known IE(Ti) has made possible the determination of the difference between the 0 K bond dissociation energy (D{sub 0}) of TiC{sup +}(X{sup 2}Σ{sup +}) and that of TiC(X{sup 3}Σ{sup +}) to be D{sub 0}(Ti{sup +}−C) − D{sub 0}(Ti−C) = 0.2322(2) eV. Similar to previous experimental observations, the present state-to-state PFI-PE study of the photoionization transitions, TiC{sup +}(X{sup 2}Σ{sup +}; v{sup +} = 0 and 1, N{sup +}) ← TiC({sup 3}Π{sub 1}; v′, J′), reveals a strong decreasing trend for the photoionization cross section as |ΔN{sup +}| = |N{sup +} – J′| is increased. The maximum |ΔN{sup +}| change of 7 observed here is also consistent with the previous experimental results for the 3d transition-metal carbides, oxides, and nitrides. However, the VIS-UV-PFI-PE spectra for TiC{sup +}(X{sup 2}Σ{sup +}; v{sup +} = 0 and 1, N{sup +}) are found to display only the negative ΔN{sup +} (N{sup +}–J′≤ 0) transitions, indicating that the cross sections for the formation of positive ΔN{sup +} (N{sup +}–J′ > 0) transitions by both the channel coupling mechanism and direct photoionization are negligibly small.« less
Authors:
; ; ; ;  [1] ;  [2]
  1. Department of Chemistry, University of California, Davis, California 95616 (United States)
  2. Department of Earth and Planetary Sciences, University of California, Davis, California 95616 (United States)
Publication Date:
OSTI Identifier:
22436579
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 141; Journal Issue: 14; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BOND LENGTHS; CATIONS; CROSS SECTIONS; DISSOCIATION ENERGY; ELECTRONIC STRUCTURE; EXCITATION; GROUND STATES; NITROGEN IONS; OXIDES; PHOTOIONIZATION; POSITRONS; RESONANCE; SPECTRA; TITANIUM CARBIDES; TRANSITION ELEMENTS; VIBRATIONAL STATES