Institute of Chemical Physics, Beijing Institute of Technology, Beijing 100081, People's Republic of China.
J Chem Phys. 2010 Jan 28;132(4):044308. doi: 10.1063/1.3273321.
The unique importance of the cyclopropenylidene molecule conveys significance to its low-lying isomers. Eleven low-lying electronic triplet stationary points as well as the two lowest singlet structures of C(3)H(2) have been systematically investigated. This research used coupled cluster (CC) methods with single and double excitations and perturbative triple excitations [CCSD(T)] and Dunning's correlation-consistent polarized valence cc-pVXZ (where X=D, T, and Q) basis sets. Geometries, dipole moments, vibrational frequencies, and associated infrared intensities of the targeted molecules have been predicted. The electronic ground state of cyclopropenylidene (3S, the global minimum) is the X (1)A(1) state with C(2v) point group symmetry. Among the 11 triplet stationary points, 7 structures are found to be minima, 2 structures to be transition states, and 2 structures to be higher-order saddle points. For the six lowest-lying triplet structures and singlet propadienylidene (2S), relative energies (zero-point vibrational energy corrected values in parentheses) with respect to the global minimum [ X (1)A(1) (3S)] at the cc-pVQZ-UCCSD(T) level of theory are predicted to be propynylidene (3)B(1aT)15.5(11.3)<propadienylidene[(1)A(1)(2S)]14.2(13.3)<propadienylidene[(3)B(1)(2T)]45.0(43.8)<cyclopropenylidene[(3)A(3aT)]53.8(52.5)<cyclopropyne[(3)B(2)(4aT)]70.0(70.6)<cyclopropenylidene [(3)B(1)(3cT)]71.2(69.9)<trans-propenediylidene [(3)A(")(5T)]73.6(70.7) kcal mol(-1). The combined energy for the [C((3)P)+C(2)H(2)(X (1)Sigma(g) (+))] system with respect to the global minimum (3S) is determined to be 107.4(103.8) kcal mol(-1). Therefore, these six triplet equilibrium structures are all energetically well below the dissociation limit to [C((3)P)+C(2)H(2)(X (1)Sigma(g) (+))].
环丙烯烯分子的独特重要性赋予了其低能异构体重要意义。本文系统研究了 11 个低能三重态电子驻点以及 C(3)H(2)的两个最低单重态结构。研究采用单重态和双重激发以及微扰三重激发的耦合簇（CC）方法[CCSD(T)]和 Dunning 的相关一致极化价 cc-pVXZ（其中 X=D、T 和 Q）基组。预测了目标分子的几何形状、偶极矩、振动频率和相关红外强度。环丙烯烯（3S，全局最小值）的电子基态是具有 C(2v)点群对称性的 X（1）A(1)态。在 11 个三重态驻点中，有 7 个结构是最低点，2 个结构是过渡态，2 个结构是更高阶的鞍点。对于六个最低三重态结构和单重态丙二烯烯（2S），相对于全局最小值[X（1）A(1)（3S）]的相对能量（在 cc-pVQZ-UCCSD(T)理论水平上，零点振动能校正值）预测为炔丙基（3）B(1aT)15.5（11.3）<丙二烯烯[(1)A(1)(2S)]14.2（13.3）<丙二烯烯[(3)B(1)(2T)]45.0（43.8）<环丙烯烯[(3)A(3aT)]53.8（52.5）<环丙炔[(3)B(2)(4aT)]70.0（70.6）<环丙烯烯 [(3)B(1)(3cT)]71.2（69.9）<反式丙二烯烯 [(3)A(")(5T)]73.6（70.7）千卡·摩尔(-1)。相对于全局最小值（3S），[C((3)P)+C(2)H(2)(X（1）Σ(g)(+)）]体系的总能量确定为 107.4（103.8）千卡·摩尔(-1)。因此，这六个三重态平衡结构的能量都远低于[C((3)P)+C(2)H(2)(X（1）Σ(g)(+)）]的离解极限。
