Rajak Karunamoy, Tiwari Ashwani K
Department of Chemical Science, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, India.
J Chem Phys. 2024 Oct 14;161(14). doi: 10.1063/5.0224103.
Nonadiabatic quantum dynamics are carried out to illustrate the photoionized spectrum of the cyanopropyne (CH3-C≡C-C≡N) as reported in recent experimental measurements [Lamarre et al., J. Mol. Spectrosc. 315, 206 (2015)]. A detailed electronic structure calculation is performed to analyze the topographical details of the first five ionized states, of which three are degenerate states (X̃2E, B̃2E, and C̃2E) and two are non-degenerate states (Ã2A1 and D̃2A1). The degenerate E states of the C3V symmetry molecule are prone to Jahn-Teller (JT) instability, and in addition, symmetry allowed A1 - E vibronic coupling, i.e., pseudo-Jahn-Teller (PJT), effects are expected to have a significant impact in the detailed vibronic structure of these electronic states. The JT splittings of X̃2E and B̃2E degenerate states are small, whereas it is quite large at three high frequencies in the C̃2E electronic states. The large energy separation of X̃2E from the other states and the non-zero PJT coupling of the B̃2E state with the close-lying Ã2A1 state indicate the uncoupled nature of the X̃, Ã, and B̃ vibronic bands of C4H3N. The intersection minima of B̃ and C̃ states with the D̃ state nearly coincide with the energetic minimum of D̃ state. Therefore, the PJT couplings among these states will lead to a strong vibronic interaction to shape the respective band structure. To completely understand the JT and PJT interactions in the photoionized spectrum of C4H3N, the vibronic coupling model Hamiltonian was constructed to perform nuclear dynamics studies for these electronic states. The vibrational progressions in each vibronic band are identified and compared with the available experimental data in the literature. The impacts of JT and PJT effects in the first five ionized states of cyanopropyne are investigated and discussed in detail.
进行非绝热量子动力学计算以阐释丙炔腈（CH3 - C≡C - C≡N）的光电离光谱，该光谱已在近期的实验测量中报道[拉马尔等人，《分子光谱学杂志》315, 206 (2015)]。进行了详细的电子结构计算以分析前五个电离态的地形细节，其中三个是简并态（X̃2E、B̃2E和C̃2E），两个是非简并态（Ã2A1和D̃2A1）。具有C3V对称性的分子的简并E态易于出现 Jahn - Teller（JT）不稳定性，此外，对称性允许的A1 - E振动电子耦合，即赝 Jahn - Teller（PJT）效应，预计会对这些电子态的详细振动电子结构产生重大影响。X̃2E和B̃2E简并态的JT分裂很小，而在C̃2E电子态的三个高频处则相当大。X̃2E与其他态的大能量间隔以及B̃2E态与紧邻的Ã2A1态的非零PJT耦合表明C4H3N的X̃、Ã和B̃振动电子带的非耦合性质。B̃和C̃态与D̃态交点的最小值几乎与D̃态的能量最小值重合。因此，这些态之间的PJT耦合将导致强烈的振动电子相互作用，从而塑造各自的能带结构。为了全面理解C4H3N光电离光谱中的JT和PJT相互作用，构建了振动电子耦合模型哈密顿量以对这些电子态进行核动力学研究。确定了每个振动电子带中的振动进展，并与文献中现有的实验数据进行了比较。详细研究和讨论了JT和PJT效应在丙炔腈前五个电离态中的影响。
