Rovibronically selected and resolved two-color laser photoionization and photoelectron study of titanium monoxide cation

Abstract

Two-color visible-ultraviolet (VIS-UV) resonance-enhanced laser photoionization and pulsed field ionization-photoelectron (PFI-PE) study of gaseous titanium monoxide (TiO) in the total energy range of 55,000-57,320 cm(-1) has been conducted. The TiO molecules were selectively excited to single J' rotational levels of the intermediate TiO*(B(3)Π1, ν' = 0) state by using a VIS dye laser and then ionized by using another UV laser. This two-color photoexcitation method has allowed the measurement of cleanly J(+)-resolved PFI-PE spectra for the TiO(+)(X (2)Δ(5/2,3/2); v(+) = 0, 1, and 2) vibrational bands. By simulating the rotationally resolved PFI-PE spectra, J(+) = 3∕2 is determined to be the lowest rotational level of the ground electronic state, confirming that the symmetry of the TiO(+) ground state is (2)Δ(3/2). Irregular intensity patterns for rotational PFI-PE peaks that deviated from the regular patterns that favor the rotational transitions with small change of the core rotational angular momentum, are observed. This observation is indicative of strong perturbations of the PFI-PE rotational transitions, possibly by a channel-coupling mechanism. The analysis of the PFI-PE spectra yields highly precise values for the adiabatic ionization energy of TiO [IE(TiO) = 55 005.4 ± 0.8 cm(-1) (6.81980 ± 0.00010 eV)], and the vibrational frequency (ωe(+) = 1056.1 ± 0.8 cm(-1)), the anharmonicity constant (ωe(+)χe(+) = 4.4 ± 0.8 cm(-1)), the rotational constants (B(e)(+) = 0.5613 ± 0.0009 cm(-1) and αe(+) = 0.0029 ± 0.0008 cm(-1)), and the equilibrium bond length (r(e)(+) = 1.583 Å) for the TiO(+)(X (2)Δ(3/2)) ground state, the vibrational frequency (ωe(+) = 1058.4 ± 0.8 cm(-1)), the anharmonicity constant (ωe(+)χe(+) = 5.1 ± 0.8 cm(-1)), the rotational constants (B(e)(+) = 0.5715 ± 0.0007 cm(-1) and αe(+) = 0.0030 ± 0.0004 cm(-1)) and the equilibrium bond length (r(e)(+) = 1.568 Å) for the excited spin orbit state TiO(+)(X (2)Δ(5/2)), along with the spin-orbit coupling constant (A = 105.9 ± 0.2 cm(-1)) for TiO(+)(X (2)Δ(5/2,3/2)).