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

Abstract

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)Π1) ← TiC(X(3)Σ(+)) and TiC((3)Σ(+)) ← TiC(X(3)Σ(+)) transition bands. This assignment supports that the electronic configuration and term symmetry for the neutral TiC ground state are …7σ(2)8σ(1)9σ(1)3π(4) (X(3)Σ(+)). The rotational constant and the corresponding bond distance of TiC(X(3)Σ(+); v″ = 0) are determined to be B0″ = 0.6112(10) cm(-1) and r0″ = 1.695(2) Å, 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 …7σ(2)8σ(1)3π(4) (X(2)Σ(+)) 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 α(e)(+) = 0.0085(28) cm(-1). The latter rotational constants yield the equilibrium bond distance of r(e)(+) = 1.667(4) Å for TiC(+)(X(2)Σ(+)). 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 (D0) of TiC(+)(X(2)Σ(+)) and that of TiC(X(3)Σ(+)) to be D0(Ti(+)-C) - D0(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)Σ(+); v(+) = 0 and 1, N(+)) ← TiC((3)Π1; v', J'), reveals a strong decreasing trend for the photoionization cross section as |ΔN(+)| = |N(+) - J'| is increased. The maximum |ΔN(+)| 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)Σ(+); v(+) = 0 and 1, N(+)) are found to display only the negative ΔN(+) (N(+)-J'≤ 0) transitions, indicating that the cross sections for the formation of positive ΔN(+) (N(+)-J' > 0) transitions by both the channel coupling mechanism and direct photoionization are negligibly small.

Rotationally Resolved State-to-State Photoelectron Study of Molybdenum Monoxide Cation (MoO+)

“…The maximum transition intensities are observed at the J + = 6.5–8.5 and 7.5–9.5 states in Figures and , respectively, with the J + intensity decreasing to lower as well as higher J + values. The intensity patterns of rotational transitions observed here are consistent those found previously in the PFI–PE study of other molecules, − ,, indicating that the most favorable transitions are those with the smallest |Δ J + | value. The maximum |Δ J + | = | J + – J ′| changes of 6.5–7.5 determined here for the MoO/MoO + photoionization system are also in line with those observed in previous studies. , For Δ J + < 0 or J + < J ′ transitions, the channel coupling mechanism ,, has been used to rationalize the observation of a wide range of Δ J + rotational transitions.…”

“…An inverse autoionization mechanism has also been proposed for Δ J + > 0 or J + > J ′ transitions. Based on experimental observations, − ,,,, the Δ J + > 0 transition is less efficient than the Δ J + < 0 transition. The Δ J + > 0 transition is usually limited to Δ J + = 1–3; but in an extreme case, such as TiC/TiC + , only the Δ J + < 0 transition is observed and the Δ J + > 0 transition is found to have negligible intensities.…”

“…To obtain accurate energetic and spectroscopic data, such as ionization energies (IEs), 0 K bond dissociation energies ( D 0 ’s), rotational and vibrational constants, and fine-structure splitting constants, for transition-metal-containing species and their cations, we have undertaken rotationally resolved state-to-state photoionization and photoelectron studies of a series of 3d-transition-metal carbides, nitrides, and oxides, including FeC, NiC, CoC, TiC, TiO, VC, and VN. − Parallel to this experimental effort, we have also been performing high-level ab initio quantum calculations based on the coupled cluster theory with electronic excitations up to quadruple (CCSDTQ), along with applying the complete basis set (CBS) technique (CCSDT/CBS). Highly precise energetic data and spectroscopic constants for FeC + , NiC + , CoC + , and VC + cations obtained in two-color visible–ultraviolet (vis–UV) pulsed field ionization–photoelectron (PFI–PE) measurements were compared to theoretical CCSDTQ/CBS predictions, showing that the CCSDTQ/CBS procedure is capable of providing reliable energetic and spectroscopic predictions for these 3d-transition-metal-containing molecules and their cations. ,− The error limits for CCSDTQ/CBS IE predictions are found to fall within ±30 meV.…”

High-Level Ab Initio Predictions for the Ionization Energy, Bond Dissociation Energies, and Heats of Formation of Vanadium Methylidyne Radical and Its Cation (VCH/VCH+)

“…For a decade, we have been successfully employing the two-color laser photoionization efficiency and pulsed field ionization-photoelectron (PFI-PE) methods to unequivocally characterize many diatomic MX/MX + (X = C, N, and O) species, yielding IE­(MX) values and spectroscopic constants of the MX + cations with unprecedented accuracy. − These reliable data have enabled our definitive benchmarking for state-of-the-art ab initio calculations of the MX/MX + systems, namely, FeC/FeC + , NiC/NiC + , CoC/CoC + , TiO/TiO + , TiC/TiC + , VC/VC + , VN/VN + , VO/VO + , MoO/MoO + , NbC/NbC + , and ZrO/ZrO + . ,,− The essence of our quantum chemical procedure CCSDTQ/CBS aims to approximate the complete basis set (CBS) limit at the CC level up to quadruple excitations. The extrapolated CCSD­(T) energies are refined with the incorporation of zero-point vibrational energy (ZPVE) corrections, the high-order correlation (HOC) beyond the CCSD­(T) wave function, the core–valence (CV) electronic corrections (up to CCSDT level), and the SO and SR corrections (up to CCSDTQ level).…”

Millimeter-wave spectroscopy of CrC (X3Σ−) and CrCCH (X̃ 6Σ+): Examining the chromium-carbon bond

“…8 In the case of the diatomic carbides, optical spectroscopy has been carried out for FeC, CoC, NiC, VC, and, more recently, TiC. [10][11][12][13][14] Pure rotational data have been recorded for FeC, CoC, and NiC as well. 15,16 These studies have demonstrated that the ground states of these molecules are 3 ∆, 2 Σ + , 1 Σ + , 2 ∆, and 3 Σ + , respectively.…”