乙炔二锂(C_2Li_2)异构体反应的分子轨道研究(英文)

MOLECULAR ORBITAL STUDY OF THE ISOMERIZATION REACTION OF DILITHIOACETYLENE(C 2Li 2)

基于量子化学从头计算法（ＣＣＳＤ（Ｔ）、ＱＣＩＳＤ（Ｔ））以及二阶微扰法（ＭＰ２），研究了乙炔二锂分子的平面桥式与线性式之间的异构化途径．６－３１１Ｇ（ｄ）基态被用于几何优化和反应途径的确定，而６－３１Ｇ（３ｄｆ）基态被用于单点式计算．其有关结构优先及成键特征的结果与用Ｍφｌｅｒ－Ｐｌｅｓｓｅｔ微扰方法所得一致．在ＭＰ２／６－３１１Ｇ（ｄ）理论水平上给出了质－权坐标的最小能量途径．在本研究的最高理论水平［ＱＣＩＳＤ（Ｔ，ＦＵＬＬ）／６－３１Ｇ（３ｄｆ）∥ＱＣＩＳＤ（Ｔ，ＦＵＬＬ）／６－３１１Ｇ（ｄ）］上，发现平面型分子的异构化势垒（１０．０ｋｃａｌ／ｍｏｌ）要比线型Ｃ２Ｌｉ２（１．

High level coupled cluster(CC)based on ab initio methods, the coupled cluster singles and doubles method including non variational treatment of triple excitations(CCSD(T)) and the quadratic configuration interaction including single and double substitutions with a triple contribution(QCISD(T))methods,as well as a second order perturbation(MP2) method are applied to the study of the isomerization pathway between the planar bridged and linear dilithioacetylene(C 2Li 2) mole cule. A 6 311G(d) basis set is used in geometry optimization and reaction path determination while a 6 31G(3df) basis set is employed in single point calculations. The results on the structural preference and bonding characteristic are consistent with that obtained with MΦller Plesset perturbation methods.The minimum energy path in the mass weighted coordinates is mapped out at MP2/6 311G(d) level of theory. At the highest level of theory in this work, QCISD(T,FULL)/6 31G(3df)∥QCISD(T,FULL)/6 311G(d), it is found that the isomerization barrier for the planar species (10.0 kcal/mol) is much higher than that for the linear C 2Li 2(1.3 kcal/mol).