Fishchuk Anna V, Merritt Jeremy M, Groenenboom Gerrit C, Avoird Ad van der
Theoretical Chemistry, IMM, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
J Phys Chem A. 2007 Aug 9;111(31):7270-81. doi: 10.1021/jp0684978. Epub 2007 Jun 14.
Rovibronic energy levels and properties of the Br(2P)-HCN complex were obtained from three-dimensional calculations, with HCN kept linear and the CN bond frozen. All diabatic states that correlate to the 2P3/2 and 2P1/2 states of the Br atom were included and spin-orbit coupling was taken into account. The 3 x 3 matrix of diabatic potential surfaces was taken from the preceding paper (paper 1). In agreement with experiment, we found two linear isomers, Br-NCH and Br-HCN. The calculated binding energies are very similar: D0 = 352.4 cm(-1) and D0 = 349.1 cm(-1), respectively. We established, also in agreement with experiment, that the ground electronic state of Br-NCH has |Omega| = (1/2) and that Br-HCN has a ground state with |Omega| = (3/2), where the quantum number, Omega, is the projection of the total angular momentum, J, of the complex on the intermolecular axis R. This picture can be understood as being caused by the electrostatic interaction between the quadrupole of the Br(2P) atom and the dipole of HCN, combined with the very strong spin-orbit coupling in Br. We predicted the frequencies of the van der Waals modes of both isomers and found a direct Renner-Teller splitting of the bend mode in Br-HCN and a smaller, indirect, splitting in Br-NCH. The red shift of the CH stretch frequency in the complex, relative to free HCN, was calculated to be 1.98 cm(-1) for Br-NCH and 23.11 cm(-1) for Br-HCN, in good agreement with the values measured in helium nanodroplets. Finally, with the use of the same potential surfaces, we modeled the Cl(2P)-HCN complex and found that the experimentally observed linear Cl-NCH isomer is considerably more stable than the (not observed) Cl-HCN isomer. This was explained mainly as an effect of the substantially smaller spin-orbit coupling in Cl, relative to Br.
通过三维计算得到了Br(2P)-HCN复合物的振转电子能级和性质，其中HCN保持线性且CN键固定。考虑了所有与Br原子的2P3/2和2P1/2态相关的非绝热态，并计入了自旋轨道耦合。非绝热势能面的3×3矩阵取自前文（论文1）。与实验结果一致，我们发现了两种线性异构体，即Br-NCH和Br-HCN。计算得到的结合能非常相似：分别为D0 = 352.4 cm(-1)和D0 = 349.1 cm(-1)。我们还与实验结果一致地确定，Br-NCH的基电子态的|Ω| = (1/2)，而Br-HCN的基态的|Ω| = (3/2)，其中量子数Ω是复合物的总角动量J在分子间轴R上的投影。这种情况可以理解为由Br(2P)原子的四极矩与HCN的偶极矩之间的静电相互作用，再加上Br中非常强的自旋轨道耦合所导致。我们预测了两种异构体的范德华模式频率，并发现Br-HCN中弯曲模式存在直接的伦纳-泰勒分裂，而Br-NCH中的分裂较小且为间接分裂。相对于自由HCN，复合物中CH伸缩频率的红移对于Br-NCH计算为1.98 cm(-1)，对于Br-HCN计算为23.11 cm(-1)，与在氦纳米液滴中测量的值非常吻合。最后，使用相同的势能面，我们对Cl(2P)-HCN复合物进行了建模，发现实验观察到的线性Cl-NCH异构体比（未观察到的）Cl-HCN异构体稳定得多。这主要解释为Cl相对于Br的自旋轨道耦合显著较小的效应。
