Liang Yue, Fábri Csaba, Su Junjie, Billinghurst Brant, Zhao Jianbao, Chen Ziqiu, Liu Bowen
College of Chemistry and Chemical Engineering, Lanzhou University, 222 South Tianshui Rd., Lanzhou 730000, China.
HUN-REN-ELTE Complex Chemical Systems Research Group, P.O. Box 32, H-1518 Budapest 112, Hungary.
J Chem Phys. 2024 Sep 7;161(9). doi: 10.1063/5.0228249.
The pure rotational and rovibrational spectra of the ν27 -NH2 torsion of cyclopropylamine (CPA) in the far-infrared region were measured with a high-resolution Fourier transform infrared coupled to a synchrotron. The complex spectra reflect the presence of both trans and gauche conformers. Analysis of the pure rotational spectra (34-64 cm-1) yielded accurate rotational and centrifugal distortion constants of the ground and first two torsional excited states of trans-CPA. The fundamental, hot bands and weak overtones were identified and assigned in the 200-550 cm-1 range. Global analysis of over 19 000 transitions provides accurate energy levels of the torsional polyads up to vT = 3. The torsional levels and their rotational constants were in agreement with the theoretical results from quasiadiabatic channel reaction path Hamiltonian (RPH) calculations, emphasizing the need for molecular-specific theoretical treatments for large amplitude motions. Tunneling components of the torsional fundamental of gauche-CPA were assigned based on the RPH results and symmetry considerations, differing from previous experimental and theoretical work. This comprehensive spectroscopic characterization of CPA is crucial for its potential detection in the interstellar medium as a precursor to complex prebiotic molecules, providing essential data for future astronomical searches and advancing our understanding of nitrogen-containing organic molecules in space.
利用与同步加速器耦合的高分辨率傅里叶变换红外光谱仪，测量了环丙胺（CPA）在远红外区域的ν27 -NH₂扭转的纯转动光谱和振转光谱。复杂的光谱反映了反式和顺式构象体的存在。对纯转动光谱（34 - 64厘米⁻¹）的分析得出了反式CPA基态和前两个扭转激发态的精确转动常数和离心畸变常数。在200 - 550厘米⁻¹范围内识别并归属了基频、热谱带和弱泛频。对超过19000个跃迁的全局分析提供了高达vT = 3的扭转多重组的精确能级。扭转能级及其转动常数与准绝热通道反应路径哈密顿量（RPH）计算的理论结果一致，强调了对大幅运动进行分子特异性理论处理的必要性。基于RPH结果和对称性考虑，归属了顺式CPA扭转基频的隧穿成分，这与之前的实验和理论工作不同。CPA的这种全面光谱表征对于其在星际介质中作为复杂益生元前体分子的潜在探测至关重要，为未来的天文搜索提供了重要数据，并增进了我们对太空中含氮有机分子的理解。
