物理化学学报 >> 2013, Vol. 29 >> Issue (03): 473-478.doi: 10.3866/PKU.WHXB201212273

热力学，动力学和结构化学 上一篇    下一篇

“宇称-时间不对称”的实验探索: 手性丙氨酸单晶N+H…O氢键的电子自旋翻转相变的不对称拉曼散射

王文清1, 龚1,2, 沈新春1, 张玉凤1,2   

  1. 1 北京大学化学与分子工程学院应用化学系, 北京分子科学国家实验室, 北京 100871;
    2 北京服装学院材料科学与工程学院, 北京 100029
  • 收稿日期:2012-11-13 修回日期:2012-12-24 发布日期:2013-02-25
  • 通讯作者: 王文清 E-mail:wangwqchem@pku.edu.cn
  • 基金资助:

    国家自然科学基金(21002006, 20452002)和国家科技部基础研究重大项目(2004-973-36)资助

Experimental Test of“Parity-Time Asymmetry”in Electron Spin-Flip Raman Scattering of the N+H…O Hydrogen Bond in Chiral Alanine Crystals

WANG Wen-Qing1, GONG Yan1,2, SHEN Xin-Chun1, ZHANG Yu-Feng1,2   

  1. 1 Beijing National Laboratory for Molecular Sciences, Department of Applied Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China;
    2 School of Materials Science & Engineering, Beijing Institute of Fashion Technology, Beijing 100029, P. R. China
  • Received:2012-11-13 Revised:2012-12-24 Published:2013-02-25
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (21002006, 20452002) and Special Program for Key Basic Research of the Ministry of Science and Technology, China (2004-973-36).

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摘要：

手性丙氨酸单晶的极性N+H…O氢键在~270 K的自发对称性破缺, 可用变温拉曼振动光谱在b(cc)b几何条件下在线测定. 由于其对手性的灵敏度, 可以测定D-和L-丙氨酸的N+H…O氢键在电子自旋翻转相变时的微小能差. 晶体定向能量的正/负, 在于电子自旋的上/下转向, 取决于原子内在磁场的方向. 变温拉曼振动光谱可以观察到: 在D-和L-丙氨酸单晶之间, 拉曼散射光子的波数位移方向相反, 散射光子的不对称度约为1/3. 由于自旋是轴矢量, 样品必须是单晶, 沿轴向测定. 多晶粉末不能观察到相变. 与次甲基(Cα－H)在260 K的自旋翻转相变, 用变温拉曼振动光谱在c(aa)c 几何条件下的相对测量结果接近一致. 本实验提供了一条证明真实手性和“宇称-时间(PT)不对称”的新线索.

关键词: 宇称-时间不对称, 自发对称性破缺, 不对称拉曼散射, 极性N+H…O氢键, 次甲基, 电子自旋翻转相变, 真实手性, D-和L-丙氨酸单晶

Abstract:

Spontaneous symmetry breaking of the N+H…O bond in chiral alanine crystals around 270 K was detected in situ by Raman vibrational scattering with b(cc)b geometry. An electron spin-flip transition of the N+H…O mode in D-/L-alanine was observed by the scattering of light with left/right orientation and its spin projection antiparallel to the direction of propagation. It is an internal magnetic field originated from the spin-orbit interaction. An obvious Raman wavenumber shift with opposite in sign and roughly one third of the asymmetry (A) of the scattered photon between D- and L-alanine crystals was observed. This shift was not seen in polycrystalline powder measurements because spin is an axial vector. An electron spin-flip transition of the methyne (Cα－H) mode around 260 K was shown to be approximative coincidence by examining the temperature-dependent relative intensity of asymmetric Raman scattering with c(aa)c geometry. This article provides evidence for the true chirality and parity-time (PT) asymmetry in molecular clusters of D- and L-alanine crystals.

Key words: Parity-time asymmetry, Spontaneous symmetry breaking, Asymmetric Raman scattering, Polar N+H…O bond, Methyne, Electron spin-flip transition, True chirality, D- and L-alanine crystals