Sreeruttun Raj K, Ramasami Ponnadurai, Wannere Chaitanya S, Simmonett Andrew C, Schaefer Henry F
Department of Chemistry, Faculty of Science, University of Mauritius, Republic of Mauritius, and Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, USA.
J Phys Chem A. 2008 Apr 3;112(13):2838-45. doi: 10.1021/jp0763329. Epub 2008 Mar 12.
Molecular structures, energetics, vibrational frequencies, and electron affinities are predicted for the phenylethynyl radical and its isomers. Electron affinities are computed using density functional theory, -namely, the BHLYP, BLYP, B3LYP, BP86, BPW91, and B3PW91 functionals-, employing the double-zeta plus polarization DZP++ basis set; this level of theory is known to perform well for the computation of electron affinities. Furthermore, ab initio computations employing perturbation theory, coupled cluster with single and double excitations [CCSD], and the inclusion of perturbative triples [CCSD(T)] are performed to determine the relative energies of the isomers. These higher level computations are performed with the correlation consistent family of basis sets cc-pVXZ (X = D, T, Q, 5). Three electronic states are probed for the phenylethynyl radical. In C2v symmetry, the out-of-plane (2B1) radical is predicted to lie about 10 kcal/mol below the in-plane (2B2) radical by DFT methods, which becomes 9.4 kcal/mol with the consideration of the CCSD(T) method. The energy difference between the lowest pi and sigma electronic states of the phenylethynyl radical is also about 10 kcal/mol according to DFT; however, CCSD(T) with the cc-pVQZ basis set shows this energy separation to be just 1.8 kcal/mol. The theoretical electron affinities of the phenylethynyl radical are predicted to be 3.00 eV (B3LYP/DZP++) and 3.03 eV (CCSD(T)/DZP++//MP2/DZP++). The adiabatic electron affinities (EAad) of the three isomers of phenylethynyl, that is, the ortho-, meta-, and para-ethynylphenyl, are predicted to be 1.45, 1.40, and 1.43 eV, respectively. Hence, the phenylethynyl radical binds an electron far more effectively than the three other radicals studied. Thermochemical predictions, such as the bond dissociation energies of the aromatic and ethynyl C-H bonds and the proton affinities of the phenylethynyl and ethynylphenyl anions, are also reported.
对苯乙炔基自由基及其异构体的分子结构、能量、振动频率和电子亲和能进行了预测。使用密度泛函理论计算电子亲和能，即BHLYP、BLYP、B3LYP、BP86、BPW91和B3PW91泛函，并采用双ζ加极化DZP++基组；已知该理论水平在计算电子亲和能方面表现良好。此外，还进行了采用微扰理论、含单双激发的耦合簇方法[CCSD]以及包含微扰三重激发[CCSD(T)]的从头算计算，以确定异构体的相对能量。这些更高水平的计算使用了相关一致基组族cc-pVXZ（X = D、T、Q、5）。对苯乙炔基自由基研究了三个电子态。在C2v对称性下，通过密度泛函理论方法预测，面外（2B1）自由基比面内（2B2）自由基低约10千卡/摩尔，考虑CCSD(T)方法后变为9.4千卡/摩尔。根据密度泛函理论，苯乙炔基自由基最低的π和σ电子态之间的能量差也约为10千卡/摩尔；然而，使用cc-pVQZ基组的CCSD(T)方法表明该能量间隔仅为1.8千卡/摩尔。预测苯乙炔基自由基的理论电子亲和能为3.00电子伏特（B3LYP/DZP++）和3.03电子伏特（CCSD(T)/DZP++//MP2/DZP++）。预测苯乙炔基的三种异构体，即邻位、间位和对位乙炔基苯基的绝热电子亲和能（EAad）分别为1.45、1.40和1.43电子伏特。因此，苯乙炔基自由基比所研究的其他三种自由基更有效地结合电子。还报告了热化学预测结果，如芳香族和乙炔基C-H键的键解离能以及苯乙炔基和乙炔基苯基阴离子的质子亲和能。
