Chaudhuri Rajat K, Freed Karl F
Indian Institute of Astrophysics, Bangalore-560034, India.
J Chem Phys. 2008 Aug 7;129(5):054308. doi: 10.1063/1.2958282.
The ground state geometries and associated normal mode frequencies of the classical and nonclassical protonated acetylene ion, i.e., the vinyl cation C(2)H(3) (+), are computed using the complete active space self-consistent field and improved virtual orbital (IVO) complete active space configuration interaction methods. In addition, the minimum-energy reaction path for the classical to nonclassical interconversion is determined (as are excitation energies) using the IVO modification of multireference Moller-Plesset (MRMP) perturbation theory. The IVO-MRMP treatment predicts the nonclassical structure to be 4.8 kcalmol more stable than the classical one, which is consistent with other high level theoretical estimates. The proton affinity of acetylene from the IVO-MRMP treatment (154.8 kcalmol) also agrees well with experiment (153.3 kcalmol) and with earlier CASPT2 calculations (154.8 kcalmol). We further report geometries and vibrational frequencies of low lying excited states of C(2)H(3) (+), which have not been observed and/or studied before. Comparisons with previous highly correlated calculations further demonstrate the computational efficiency of the IVO-MRPT methods.
使用完全活性空间自洽场和改进的虚拟轨道（IVO）完全活性空间组态相互作用方法，计算了经典和非经典质子化乙炔离子（即乙烯基阳离子C(2)H(3) (+)）的基态几何结构及相关的简正模式频率。此外，使用多参考莫勒-普莱斯特定理（MRMP）微扰理论的IVO修正方法，确定了从经典到非经典相互转化的最小能量反应路径（以及激发能）。IVO-MRMP处理预测非经典结构比经典结构稳定4.8千卡/摩尔，这与其他高水平理论估计结果一致。IVO-MRMP处理得到的乙炔质子亲和能（154.8千卡/摩尔）也与实验值（153.3千卡/摩尔）以及早期的CASPT2计算结果（154.8千卡/摩尔）吻合良好。我们还报道了C(2)H(3) (+)低激发态的几何结构和振动频率，这些此前尚未被观测和/或研究过。与之前高度相关计算结果的比较进一步证明了IVO-MRPT方法的计算效率。
