Saha Ashim Kumar, Sarma Gautam, Yang Chung-Hsin, van de Meerakker Sebastiaan Y T, Parker David H, Western Colin M
Department of Molecular and Laser Physics, Radboud University Nijmegen, IMM-FNWI, Nijmegen, The Netherlands.
Phys Chem Chem Phys. 2015 Jun 7;17(21):14145-58. doi: 10.1039/c5cp01299f. Epub 2015 May 11.
Rotationally resolved resonance enhanced multiphoton ionisation spectra of the B̃(1)E'' state of NH2D are presented and analysed. The analysis indicates a small (34.9 cm(-1)) lifting of the vibronic degeneracy of the zero point level, approximately equal in sign but opposite in magnitude to the splitting observed in NHD2 in previous work. This observation is consistent with previous measurements on systems with partial isotopic substitution subject to a mild Jahn-Teller effect. A model is developed to calculate the splitting induced by asymmetric isotopic substitution of a degenerate electronic state, based on a harmonic force field with linear and quadratic Jahn-Teller terms added. The force field is developed in internal co-ordinates to allow the same parameters to be used to calculate the pattern of vibronic levels for all four isotopologues. The lifting of the degeneracy of the zero point level on asymmetric substitution comes from the quadratic Jahn-Teller effect; the linear term does not lift the degeneracy.
本文给出并分析了NH₂D的B̃(1)E''态的转动分辨共振增强多光子电离光谱。分析表明零点能级的振转简并度有一个小的（34.9 cm⁻¹）解除，其符号与之前工作中在NHD₂中观察到的分裂大致相同，但大小相反。这一观察结果与先前对受温和 Jahn - Teller 效应影响的部分同位素取代体系的测量结果一致。基于添加了线性和二次 Jahn - Teller 项的谐振子力场，建立了一个模型来计算简并电子态的不对称同位素取代引起的分裂。力场是在内部坐标中建立的，以便使用相同的参数来计算所有四种同位素异构体的振转能级模式。不对称取代时零点能级简并度的解除来自二次 Jahn - Teller 效应；线性项不会解除简并。
