Center for Computational Quantum Chemistry, The University of Georgia, Athens, Georgia 30602, USA.
J Chem Phys. 2018 Sep 7;149(9):094302. doi: 10.1063/1.5042763.
The peculiar electronic absorption spectrum of HCN has been of great interest to experiment. Herein, this system is studied extensively by applying theoretical methods to the ground and low-lying excited electronic states. Employing a large breadth of high-level computations, including coupled cluster [CCSD(T) and CCSDT(Q)] and multireference configuration interaction [MRCISD+Q] methods, we comprehensively demonstrate that the most recent experimental and theoretical interpretations of the electronic spectrum of HCN are in error. The previous assignments of the two broad features in the spectrum as the origin (∼35 050 cm) and (∼35 600 cm) transitions are both found to be incorrect. The presently reported transition energies suggest that the higher energy band near 35 600 cm is the true origin band. Additionally, from the computed anharmonic vibrational frequencies of the and states, we show that this ∼550 cm band spacing cannot be attributed to a simple vibronic transition, as claimed by the assignment. Possible alternative explanations for the appearance of the lower intensity band near 35 050 cm are discussed.
HCN 的特殊电子吸收光谱一直是实验研究的热点。在此，通过应用理论方法研究基态和低激发电子态，对该体系进行了广泛的研究。采用包括耦合簇 [CCSD(T) 和 CCSDT(Q)] 和多参考组态相互作用 [MRCISD+Q] 在内的广泛的高精度计算，我们全面证明了 HCN 电子光谱的最新实验和理论解释是错误的。先前将光谱中的两个宽特征分别分配为起源（约 35050cm）和（约 35600cm）跃迁的解释都是不正确的。目前报告的跃迁能量表明，在 35600cm 附近的高能带才是真正的起源带。此外，从和态的计算非谐振动频率可知，正如 分配所声称的，这个约 550cm 的带间隔不能归因于简单的振子跃迁。我们讨论了在 35050cm 附近出现低强度带的可能替代解释。
