title: High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of cobalt carbide (CoC) and its cation (CoC+).
abstract: The ionization energy (IE) of CoC and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (ΔH°f0) and 298 K (ΔH°f298) for CoC and CoC(+) are predicted by the wavefunction based coupled-cluster theory with single, double, triple and quadruple excitations (CCSDTQ) and complete basis set (CBS) approach. The CCSDTQ∕CBS calculations presented here involve the approximation to the CBS limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy, high-order correlation, core-valence (CV) electronic, spin-orbit coupling, and scalar relativistic effect corrections. The present calculations provide the correct symmetry, (1)Σ(+), for the ground state of CoC(+). The CCSDTQ∕CBS IE(CoC) = 7.740 eV is found in good agreement with the experimental IE value of 7.73467 ± 0.00007 eV, determined in a two-color laser photoion and pulsed field ionization-photoelectron study. This work together with the previous experimental and theoretical investigations support the conclusion that the CCSDTQ∕CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC, CoC, and NiC. Among the single-reference based coupled-cluster methods and multi-reference configuration interaction (MRCI) approach, the CCSDTQ and MRCI methods give the best predictions to the harmonic frequencies ωe (ωe (+)) = 956 (992) and 976 (1004) cm(-1) and the bond lengths re (re (+)) = 1.560 (1.528) and 1.550 (1.522) Å, respectively, for CoC (CoC(+)) in comparison with the experimental values. The CCSDTQ∕CBS calculations give the prediction of D0(Co(+)-C) - D0(Co-C) = 0.175 eV, which is also consistent with the experimental determination of 0.14630 ± 0.00014 eV. The theoretical results show that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of CoC∕CoC(+). For the experimental D0 and ΔH(o) f0 values of CoC∕CoC(+), which are not known experimentally, we recommend the following CCSDTQ∕CBS predictions: ΔH(o) f0(CoC) = 775.7 kJ∕mol and ΔH(o) f0(CoC(+)) = 1522.5 kJ∕mol, ΔH(o) f298(CoC) = 779.2 kJ∕mol and ΔH(o) 298(CoC(+)) = 1526.0 kJ∕mol.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong. kaichung@cityu.edu.hk
authors.forename: Kai-Chung
authors.initials: KC
authors.lastname: Lau
authors.forename: Yi
authors.initials: Y
authors.lastname: Pan
authors.forename: Chow-Shing
authors.initials: CS
authors.lastname: Lam
authors.forename: Huang
authors.initials: H
authors.lastname: Huang
authors.forename: Yih-Chung
authors.initials: YC
authors.lastname: Chang
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Luo
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Shi
authors.forename: C Y
authors.initials: CY
authors.lastname: Ng
mesh_terms: D017554:Carbon Compounds, Inorganic / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry*; D006358:Hot Temperature; D011789:Quantum Theory
chemical_list: D017554:Carbon Compounds, Inorganic; D002412:Cations; D003035:Cobalt