K. C. Liu, C. Y. Ng. Accurate ab initio Predictions of Ionization Energies and Heats of Formation for Cyclopropenylidene, Propargylene and Propadienylidene[J]. Chinese Journal of Chemical Physics , 2006, 19(1): 29-38. doi: 10.1360/cjcp2006.19(1).29.10
Citation: K. C. Liu, C. Y. Ng. Accurate ab initio Predictions of Ionization Energies and Heats of Formation for Cyclopropenylidene, Propargylene and Propadienylidene[J]. Chinese Journal of Chemical Physics , 2006, 19(1): 29-38. doi: 10.1360/cjcp2006.19(1).29.10

Accurate ab initio Predictions of Ionization Energies and Heats of Formation for Cyclopropenylidene, Propargylene and Propadienylidene

doi: 10.1360/cjcp2006.19(1).29.10
Funds:  Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research. NWChem Version 4.7,as developed and distributed by Pacific Northwest National Laboratory, P. O. Box 999, Richland, Washington 99352 USA, and the U. S. Department of Energy, was used to obtain some of these results.Part of the calculations of this work used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No.DEAC03-76SF00098. C. Y. Ng also acknowledges partial supports by the NSF CHE-0517871, AFOSR Grant No. F49620-03-1- 0116, and NSF ATM-0317422.
  • Received Date: 2005-12-27
  • The ionization energies (IEs) of cyclopropenylidene (c-C3H2), propargylene (HCCCH) and propadienylidene (H2CCC) have been computed using the CCSD(T)/CBS method, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level with single and double excitations plus quasi-perturbative triple excitation effect (CCSD(T)). The zero-point vibrational energy correction,the core-valence electronic correction, the scalar relativistic effect and the high level correction beyond the CCSD(T) excitations have also been made in these calculations. The CCSD(T)/CBS values for the IE(c-C3H2) and IE(HCCCH) of 9.164, 8.987 eV are in good agreement with the experimental values of (9.15±0.03) and (8.96±0.04) eV. The CCSD(T)/CBS calculations yield the IE values of 10.477 and 10.388eV for the ionization transitions H2CCC→H2CCC+(2A1, C2v) and H2CCC→H2CCC+(2A', Cs), respectively. On the basis of the Franck-Condon factor consideration, the IE of (10.43±0.02) eV determined in the previous single-photon ionization experiment most likely corresponds to the ionization threshold for the H2CCC→H2CCC+(2A1, C2v) transition. Although the precision of the experimental IE measurements for c-C3H2, HCCCH, and H2CCC is insufficient to pin down the accuracy of the theoretical calculations to better than ±30 meV, the excellent agreement between the experimental and theoretical IE values observed in the present study indicates that the CCSD(T)/CBS calculations together with high-order correlation corrections are capable of yielding reliable IE predictions for simple hydrocarbon carbenes and bi-radicals.We have also reported the heats of formation at 0 K (ΔHof0) and 298 K (ΔHof298) for c-C3H2/c-C3H2+,HCCCH/HCCCH+, and H2CCC/H2CCC+. The available experimental ΔHof0 and ΔHof298 values for c-C3H2/c-C3H2+, HCCCH/HCCCH+ are found to be in good accord with the CCSD(T)/CBS predictions after taking into account the experimental uncertainties.
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Accurate ab initio Predictions of Ionization Energies and Heats of Formation for Cyclopropenylidene, Propargylene and Propadienylidene

doi: 10.1360/cjcp2006.19(1).29.10
Funds:  Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research. NWChem Version 4.7,as developed and distributed by Pacific Northwest National Laboratory, P. O. Box 999, Richland, Washington 99352 USA, and the U. S. Department of Energy, was used to obtain some of these results.Part of the calculations of this work used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No.DEAC03-76SF00098. C. Y. Ng also acknowledges partial supports by the NSF CHE-0517871, AFOSR Grant No. F49620-03-1- 0116, and NSF ATM-0317422.

Abstract: The ionization energies (IEs) of cyclopropenylidene (c-C3H2), propargylene (HCCCH) and propadienylidene (H2CCC) have been computed using the CCSD(T)/CBS method, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level with single and double excitations plus quasi-perturbative triple excitation effect (CCSD(T)). The zero-point vibrational energy correction,the core-valence electronic correction, the scalar relativistic effect and the high level correction beyond the CCSD(T) excitations have also been made in these calculations. The CCSD(T)/CBS values for the IE(c-C3H2) and IE(HCCCH) of 9.164, 8.987 eV are in good agreement with the experimental values of (9.15±0.03) and (8.96±0.04) eV. The CCSD(T)/CBS calculations yield the IE values of 10.477 and 10.388eV for the ionization transitions H2CCC→H2CCC+(2A1, C2v) and H2CCC→H2CCC+(2A', Cs), respectively. On the basis of the Franck-Condon factor consideration, the IE of (10.43±0.02) eV determined in the previous single-photon ionization experiment most likely corresponds to the ionization threshold for the H2CCC→H2CCC+(2A1, C2v) transition. Although the precision of the experimental IE measurements for c-C3H2, HCCCH, and H2CCC is insufficient to pin down the accuracy of the theoretical calculations to better than ±30 meV, the excellent agreement between the experimental and theoretical IE values observed in the present study indicates that the CCSD(T)/CBS calculations together with high-order correlation corrections are capable of yielding reliable IE predictions for simple hydrocarbon carbenes and bi-radicals.We have also reported the heats of formation at 0 K (ΔHof0) and 298 K (ΔHof298) for c-C3H2/c-C3H2+,HCCCH/HCCCH+, and H2CCC/H2CCC+. The available experimental ΔHof0 and ΔHof298 values for c-C3H2/c-C3H2+, HCCCH/HCCCH+ are found to be in good accord with the CCSD(T)/CBS predictions after taking into account the experimental uncertainties.

K. C. Liu, C. Y. Ng. Accurate ab initio Predictions of Ionization Energies and Heats of Formation for Cyclopropenylidene, Propargylene and Propadienylidene[J]. Chinese Journal of Chemical Physics , 2006, 19(1): 29-38. doi: 10.1360/cjcp2006.19(1).29.10
Citation: K. C. Liu, C. Y. Ng. Accurate ab initio Predictions of Ionization Energies and Heats of Formation for Cyclopropenylidene, Propargylene and Propadienylidene[J]. Chinese Journal of Chemical Physics , 2006, 19(1): 29-38. doi: 10.1360/cjcp2006.19(1).29.10

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