Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Department of Chemistry and Biochemistry, Institute for Theoretical Chemistry, The University of Texas at Austin, Austin, Texas 78712, USA.
J Chem Phys. 2014 Jan 14;140(2):024313. doi: 10.1063/1.4859876.
Reduced dimension variational calculations have been performed for the rovibrational level structure of the S1 state of acetylene. The state exhibits an unusually complicated level structure, for various reasons. First, the potential energy surface has two accessible conformers, trans and cis. The cis conformer lies about 2700 cm(-1) above the trans, and the barrier to cis-trans isomerization lies about 5000 cm(-1) above the trans minimum. The trans vibrations ν4 (torsion) and ν6 (asym. bend) interact very strongly by Darling-Dennison and Coriolis resonances, such that their combination levels and overtones form polyads with unexpected structures. Both conformers exhibit very large x36 cross-anharmonicity since the pathway to isomerization is a combination of ν6 and ν3 (sym. bend). Near the isomerization barrier, the vibrational levels show an even-odd K-staggering of their rotational levels as a result of quantum mechanical tunneling through the barrier. The present calculations address all of these complications, and reproduce the observed K-structures of the bending and C-C stretching levels with good qualitative accuracy. It is expected that they will assist with the assignment of the irregular patterns near the isomerization barrier.
已对乙炔 S1 态的振转能级结构进行了约化维数变分计算。由于各种原因，该状态表现出异常复杂的能级结构。首先，势能面有两种可及构象，即 trans 和 cis。cis 构象位于 trans 上方约 2700 cm(-1)，cis-trans 异构化的势垒位于 trans 最低点上方约 5000 cm(-1)。trans 振动 ν4（扭转）和 ν6（不对称弯曲）通过 Darling-Dennison 和 Coriolis 共振强烈相互作用，使得它们的组合能级和泛音形成具有意外结构的多聚体。由于异构化途径是 ν6 和 ν3（对称弯曲）的组合，两种构象都表现出非常大的 x36 交叉非谐性。在异构化势垒附近，由于量子力学隧穿通过势垒，振动能级表现出其转动能级的奇偶 K 交错。目前的计算解决了所有这些复杂性，并以良好的定性精度再现了弯曲和 C-C 伸缩能级的观察到的 K 结构。预计它们将有助于分配异构化势垒附近的不规则模式。
