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Accurate ab initio Predictions of Ionization Energies and Heats of Formation for Cyclopropenylidene, Propargylene and Propadienylidene
K. C. Liu,C. Y. Ng*
Author NameAffiliation
K. C. Liu James Franck Institute and Department of Chemistry, University of Chicago, Chicago 60637 , USA 
C. Y. Ng* Department of Chemistry University of California, Davis One Shields Avenue Davis, California 95616 USA 
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.
Key words:  Ab intio, Ionization energy, Heat of formation, c-C3H2, HCCCH, H2CCC
FundProject:
c-C3H2、HCCH和H2CCC的电离能和生成热的从头算精确预示
刘佳聪,伍灼耀*
摘要:
c-C3H2,HCCH和H2CCC的电离能用CCSD(T)/CBS方法进行了计算.在计算中还包含了零点振动能校正和芯电子和价电子相关校正,标量相对论效应和高于CCSD(T)理论水平的校正.CCSD(T)/CBS方法计算的c-C3H2和HCCH电离能的数值分别为(9.15±0.03)和(8.96±0.04)eV,且与实验值(9.15+0.03)和(8.96±0.04)eV很好一致.CCSD(T)计算的H2CCC→H2CCC+(2A1,C2v)和H2CCC→H2CCC+(2A',Cs)电离跃迁的电离能分别为10.477和10.388 eV.在考虑Frank-Condon因子基础上,以前单光子电离实验所测定的(10.43±0.02)eV电离能最可能对应于H2CCC→H2CCC+(2A1,C2v)跃迁的电离阈值.虽然对c-C3H2,HCCH和H2CCC实验电离能测量的精确性难以达到理论计算精度的±30 meV范围内,所得到的理论电离能值与实验值非常一致,表明CCSD(T)/CBS计算结合高级相关校正对简单的碳氢卡宾和双自由基能得到可靠的电离能预示值.还给出了c-C3H2/c-C3H2+,HCCH/HCCH+和H2CCC/H2CCC+在0和298 K的生成热ΔHof0和ΔHof298.发现考虑实验精度不确定性后,它们的实验值与CCSD(T)/CBS预示值非常一致.
关键词:  从头算  电离能  生成热  c-C3H2  HCCH  H2CCC
DOI:10.1360/cjcp2006.19(1).29.10
分类号: