Two-Color Pulsed-Field Ionization-Photoelectron Spectroscopy: A Quest to Benchmark State-of-the-Art ab initio Quantum Electronic Structure Calculations of Spectroscopic and Energetic Properties for Transition Metal-Containing Species

We have implemented a laser ablation metal beam source for the production of supersonically cooled gaseous transition metal (M)-containing molecular species. Using this cold metal beam source, together with the application of two-color visible-ultraviolet (VIS-UV) excitation schemes, we have successfully obtained high-resolution pulsed-field-ionization-photoelectron (PFI-PE) spectra for an array of diatomic transition metal carbides, nitrides, and oxides (MX, X=C, N, and O). The quantum-rovibrational-state-selected and resolved PFI-PE spectra thus obtained have allowed unambiguous rotational analyses of these PFI-PE spectra, resulting in highly reliable spectroscopic constants and energetic properties for these MX species and their cations MX⁺ with unprecedented precision. Realizing that these highly accurate determinations are excellent benchmarks for state-of-the-art ab initio quantum chemical calculations, we have also performed extensive theoretical calculations based on state-of-the-art wave-function-based coupled-cluster theoretical procedures for comparison with experimental determinations, aiming to provide an impetus for the further development of theoretical schemes for more accurate spectroscopic and energetic predictions of M-containing species. Recent progress made in recording quantum-state-resolved PFI-PE spectra of M-containing triatomic species using single-photon vacuum ultraviolet laser and two-color VIS-UV laser excitation schemes are also discussed.