The electronic and molecular structure of radicals with a C=C core

根据理论计算，处于最低三态（T_1）的乙炔在顺式、反式和偏乙烯构型上有三个局部极小值。这些构型之间的异构化反应一直受到人们的关注。我们利用近红外二极管激光动力学光谱结合脉冲汞光敏反应，观察到在7400 cm^<-1>区域附近顺弯构型的T_2 - T_1电位表面之间的电子跃迁。目前对C_2H_2、C_2HD和C_2D_2的0-0波段进行了旋转分析，在C_2H_2最低三重态的一些特定Ka态中发现了严重的不均匀旋转微扰，但在C_2HD和C_2D_2中未观察到微扰。最低三重态中振动基态Ka=1态的扰动是一个谜。这种扰动的一个候选是其他异构体之间的相互作用。一些高水平的从头计算预测，在T_2和T_1表面都有一个小势垒的反式异构体构型上有一个更大的势垒最小值。在T_2的情况下，预计反式最小值低于顺式最小值。因此，顺式和反式之间的相互作用是可以预料的，特别是当某些振动模式被激发时。最近我们分别在8170 cm^<-1>区和7970 cm^<-1>区观测到C_2H_2和C_2D_2的1-0波段被激发出顺弯振动模式。基于组合差值的旋转分析，识别出更严重的微扰。此外，在振动激励下，C=C轴周围的旋转常数异常增大。这种强科里奥利相互作用可能暗示了异构化反应的可能性，因为Ka的旋转量子数（沿C=C轴的角动量）在包括线性构型的异构化过程中可以是常数运动。为了讨论顺式（C_<2v>）和反式（C_<2h>）构型等不同点群之间的相互作用，需要引入完全核置换反转群G_8作为通用对称平台。少

Acetylene in the lowest triplet state (T_1) has three local minima at cis, trans, and vinylidene configurations according to theoretical calculations. Isomerization reaction among those configurations has been paid a lot of attentions. We have observed an electronic transition between the T_2 - T_1 potential surface at the cis-bent configuration around 7400 cm^<-1> region by using near-IR diode laser kinetic spectroscopy combined with a pulsed mercury photo-sensitized reaction. By now 0-0 band of C_2H_2, C_2HD and C_2D_2 have been rotationally analyzed and sever inhomogeneous rotational perturbations have been recognized in some specific Ka states in the lowest triplet state of C_2H_2, but no perturbations were observed in C_2HD and C_2D_2. The perturber for the Ka=1 state of vibrational ground state in the lowest triplet state is a mystery. One candidate for this perturbation is an interaction among the other isomers. Some high level ab initio calculations predicted that there is a po … More tential minimum at the trans-isomer configuration with a small potential barrier in both the T_2 and T_1 surfaces. In case of T_2, the trans minimum is predicted to be lower than the cis. Therefore, an interaction between the cis and trans should be expected, especially when some vibrational modes are excited. Recently we have observed 1-0 band of C_2H_2 and C_2D_2 in 8170 and 7970 cm^<-1> region, respectively, in which the cis-bent vibrational mode is excited. After the rotational analysis based on the combination difference, more sever perturbations have been recognized. Moreover, the rotational constant around the C=C axis is abnormally enlarged by the vibrational excitation. This strong Coriolis type interaction may suggest a possibility of the isomerization reaction because the rotational quantum number of Ka, which is the angular momentum along the C=C axis, can be a motion of constant in the isomerization including the linear configuration. In order to discuss such an interaction between different point groups as cis (C_<2v>) and trans (C_<2h>) configurations, Complete Nuclear Permutation Inversion group G_8 should be introduced as a common symmetrical platform. Less