Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, China.
J Chem Phys. 2013 May 28;138(20):204303. doi: 10.1063/1.4806186.
Ground-state geometries of carbenes H2Cn (n = 3-10) have been fully optimized with the C2ν-symmetry constraint at the density functional theory and restricted-spin coupled-cluster single-double plus perturbative triple excitation levels of theory, respectively. Comparison of structures corresponding to the X(1)A1 and B(1)B1 electronic states has been made by the complete active space self-consistent field calculations. Parity alternation effect on various properties of the ground-state geometries has been discovered in the present study, which generally gives illustration for the relative stabilities of the titled carbon chains. Further calculations on their electronic spectra have been carried out by means of the complete active space second-order perturbation theory method along with the cc-pVTZ basis set. It is found that the vertical excitation energies of the dipole-allowed B(1)B1 ← X(1)A1 transition in the gas phase are 2.28, 4.75, 1.69, 3.66, 1.30, 2.94, 1.12, and 2.49 eV, respectively, which agree very well with the available experimental result for H2C3 (2.27 eV). In addition, the vertical excitation energies for both transitions B(1)B1 ← X(1)A1 and A(1)A2 ← X(1)A1 are found to obey a nonlinear ΔE-n relationship as a function of chain size by performing curves fitting.
卡宾 H2Cn（n = 3-10）的基态几何形状已在密度泛函理论和受限自旋耦合簇单双加微扰三激发理论水平上分别用 C2ν 对称性约束进行了完全优化。通过完全活性空间自洽场计算对对应于 X(1)A1 和 B(1)B1 电子态的结构进行了比较。本研究发现了基态几何形状各种性质的奇偶交替效应，这通常说明了标题碳链的相对稳定性。通过完全活性空间二阶微扰理论方法并结合 cc-pVTZ 基组对其电子光谱进行了进一步计算。发现气相中偶极允许的 B(1)B1 ← X(1)A1 跃迁的垂直激发能分别为 2.28、4.75、1.69、3.66、1.30、2.94、1.12 和 2.49 eV，与 H2C3（2.27 eV）的可用实验结果非常吻合。此外，通过进行曲线拟合，发现两个跃迁 B(1)B1 ← X(1)A1 和 A(1)A2 ← X(1)A1 的垂直激发能都表现出与链长有关的非线性ΔE-n 关系。
