Rovibronically selected and resolved two-color laser photoionization and photoelectron study of cobalt carbide cation

We have conducted a two-color visible-ultraviolet (VIS-UV) resonance-enhanced laser photoionization efficiency and pulsed field ionization-photoelectron (PFI-PE) study of gaseous cobalt carbide (CoC) near its ionization onset in the total energy range of 61 200-64 510 cm^-1. The cold gaseous CoC sample was prepared by a laser ablation supersonically cooled beam source. By exciting CoC molecules thus generated to single N′ rotational levels of the intermediate CoC*(²Σ ⁺; v′) state using a VIS dye laser prior to UV laser photoionization, we have obtained N⁺ rotationally resolved PFI-PE spectra for the CoC⁺(X¹Σ⁺; v⁺ = 0 and 1) ion vibrational bands free from interference by impurity species except Co atoms produced in the ablation source. The rotationally selected and resolved PFI-PE spectra have made possible unambiguous rotational assignments, yielding accurate values for the adiabatic ionization energy of CoC(X²Σ⁺), IE(CoC) = 62 384.3 ± 0.6 cm ^-1 (7.73467 ± 0.00007 eV), the vibrational frequency ω_e⁺ = 985.6 ± 0.6 cm^-1, the anharmonicity constant ω_e⁺χ_e⁺ = 6.3 ± 0.6 cm^-1, the rotational constants (B_e⁺ = 0.7196 ± 0.0005 cm^-1, α_e⁺ = 0.0056 ± 0.0008 cm^-1), and the equilibrium bond length r_e⁺ = 1.534 Å for CoC⁺(X¹Σ⁺). The observation of the N⁺ = 0 level in the PFI-PE measurement indicates that the CoC⁺ ground state is of ¹Σ⁺ symmetry. Large ΔN⁺ = N⁺ - N′ changes up to 6 are observed for the photoionization transitions CoC⁺(X¹Σ ⁺; v⁺ = 0-2; N⁺) ← CoC*( ²Σ⁺; v′; N′ = 6, 7, 8, and 9). The highly precise energetic and spectroscopic data obtained in the present study have served as a benchmark for testing theoretical predictions based on state-of-the-art ab initio quantum calculations at the CCSDTQ/CBS level of theory as presented in the companion article. © 2013 American Institute of Physics.