Rotationally resolved state-to-state photoionization and photoelectron study of titanium carbide and its cation (TiC/TiC+)

Titanium carbide and its cation (TiC/TiC+) 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(-1). Based on rotational analyses, these bands are assigned as the respective TiC((3)Pi(1)) <- TiC(X-3 Sigma(+)) and TiC((3)Sigma(+)) <- TiC(X-3 Sigma(+)) transition bands. This assignment supports that the electronic configuration and term symmetry for the neutral TiC ground state are ... 7 sigma(2)8 sigma(1)9 sigma(1)3 pi(4) (X-3 Sigma(+)). The rotational constant and the corresponding bond distance of TiC(X-3 Sigma(+); v '' = 0) are determined to be B-0 '' = 0.6112(10) cm(-1) and r(0)'' = 1.695(2) angstrom, respectively. The rotational analyses of the VIS-UV-PFI-PE spectra for the TiC+(X; v(+) = 0 and 1) vibrational bands show that the electronic configuration and term symmetry for the ionic TiC+ ground state are ... 7 sigma(2)8 sigma(1)3 pi(4) (X-2 Sigma(+)) with the v(+) = 0 -> 1 vibrational spacing of 870.0(8) cm(-1) and the rotational constants of B-e(+) = 0.6322(28) cm(-1), and alpha(+)(e) = 0.0085(28) cm(-1). The latter rotational constants yield the equilibrium bond distance of r(e)(+) = 1.667(4) angstrom for TiC+(X-2 Sigma(+)). The cleanly rotationally resolved VIS-UV-PFI-PE spectra have also provided a highly precise value of 53 200.2(8) cm(-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-0) of TiC+(X-2 Sigma(+)) and that of TiC(X-3 Sigma(+)) to be D-0(Ti+-C) - D-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+(X-2 Sigma(+); v(+) = 0 and 1, N+) <- TiC((3)Pi(1); v', J'), reveals a strong decreasing trend for the photoionization cross section as vertical bar Delta N+vertical bar = vertical bar N+ - J'vertical bar is increased. The maximum vertical bar Delta N+vertical bar 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+(X-2 Sigma(+); v(+) = 0 and 1, N+) are found to display only the negative Delta N+ (N+- J' <= 0) transitions, indicating that the cross sections for the formation of positive Delta N+ (N+- J' > 0) transitions by both the channel coupling mechanism and direct photoionization are negligibly small. (C) 2014 AIP Publishing LLC.