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Lau KC, Chang YC, Lam CS, et al. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formations of iron carbide (FeC) and its cation (FeC+). J Phys Chem A. 2009;113(52):14321-8doi: 10.1021/jp903218h.
Lau, K. C., Chang, Y. C., Lam, C. S., & Ng, C. Y. (2009). High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formations of iron carbide (FeC) and its cation (FeC+). The journal of physical chemistry. A, 113(52), 14321-8. https://doi.org/10.1021/jp903218h
Lau, Kai-Chung, et al. "High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formations of iron carbide (FeC) and its cation (FeC+)." The journal of physical chemistry. A vol. 113,52 (2009): 14321-8. doi: https://doi.org/10.1021/jp903218h
Lau KC, Chang YC, Lam CS, Ng CY. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formations of iron carbide (FeC) and its cation (FeC+). J Phys Chem A. 2009 Dec 31;113(52):14321-8. doi: 10.1021/jp903218h. PMID: 19775110.
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J Phys Chem A. 2009 Dec 31;113(52):14321-8. doi: 10.1021/jp903218h.

High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formations of iron carbide (FeC) and its cation (FeC+).

The journal of physical chemistry. A

Kai-Chung Lau, Yih-Chung Chang, Chow-Shing Lam, C Y Ng

Affiliations

  1. Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong. [email protected]

PMID: 19775110 DOI: 10.1021/jp903218h

Abstract

The ionization energy (IE) of FeC and the 0 K bond dissociation energies (D(0)) and the heats of formation at 0 K (DeltaH(o)(f0)) and 298 K (DeltaH(o)(f298)) for FeC and FeC(+) are predicted by the single-reference wave function based CCSDTQ(Full)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations. The zero-point vibrational energy (ZPVE) correction, the core-valence electronic corrections (up to CCSDT level), spin-orbit couplings, and relativistic effects (up to CCSDTQ level) are included in the calculations. The present calculations provide the correct symmetry predictions for the ground states of FeC and FeC(+) to be (3)Delta and (2)Delta, respectively. We have also examined the theoretical harmonic vibrational frequencies of FeC/FeC(+) at the ROHF-UCCSD(T) and UHF-UCCSD(T) levels. While the UHF-UCCSD(T) harmonic frequencies are in good agreement with the experimental measurements, the ROHF-UCCSD(T) yields significantly higher harmonic frequency predictions for FeC/FeC(+). The CCSDTQ(Full)/CBS IE(FeC) = 7.565 eV is found to compare favorably with the experimental IE value of 7.59318 +/- 0.00006 eV, suggesting that the single-reference-based coupled cluster theory is capable of providing reliable IE prediction for FeC, despite its multireference character. The CCSDTQ(Full)/CBS D(0)(Fe(+)-C) and D(0)(Fe-C) give the prediction of D(0)(Fe(+)-C) - D(0)(Fe-C) = 0.334 eV, which is consistent with the experimental determination of 0.3094 +/- 0.0001 eV. The D(0) calculations also support the experimental D(0)(Fe(+)-C) = 4.1 +/- 0.3 eV and D(0)(Fe-C) = 3.8 +/- 0.3 eV determined by the previous ion photodissociation study. The present calculations also provide the DeltaH(o)(f0)(DeltaH(o)(f298)) predictions for FeC/FeC(+). The analysis of the correction terms in these calculations shows that the core-valence and valence-valence electronic correlations beyond CCSD(T) wave function and the relativistic effects make significant contributions to the calculated thermochemical properties of FeC/FeC(+). For the experimental D(0) and DeltaH(o)(f0) values of FeC/FeC(+), which are not known to high precision, we recommend the CCSDTQ(Full)/CBS predictions [D(0)(Fe-C) = 3.778 eV, D(0)(Fe(+)-C) = 4.112 eV, DeltaH(o)(f0)(FeC) = 760.8 kJ/mol and DeltaH(o)(f0)(FeC(+)) = 1490.6 kJ/mol] based on the ZPVE corrections using the experimental vibrational frequencies of FeC and FeC(+).

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