Temperature-Dependent Optical Activity and Birefringence Study of D-Alanine Single Crystal
LI Zong-sheng1,GONG Yan2 ,WANG Wen-qing2,DU Wei-min1*
1. Institute of Modern Optics, School of Physics, Peking University, Beijing 100871, China 2. Institute of Applied Chemistry, College of Chemistry, Peking University, Beijing 100871, China
Abstract：The measurement of the anisotropy of optical acitivity and birefringence is one of the most important clues to studying physical properties of a biaxial crystal of D-alanine. In order to investigate a second-order phase transition predicted by A. Salam between two states of D-alanine, the behavior of birefringence and optical activity is useful for the phenomenological approach to the transition mechanism. The optical activity as a peculiar quantity can respond to the modulation of the crystal lattice and to the change in the bonding nature of constituent atoms. In the present paper, the authors use the PEM-90 photoelastic modulator to study the conformation change of D-alanine at the temperature ranging from 220 to 290 K. The temperature dependence of I2f/Idc showed that the conformation of D-alanine molecule in single crystal changed around 250 K. The obtained results provide an obvious evidence of optical rotation phase transition predicted by Salam.
Key words：D-alanine single crystal;PEM(photoelastic modulator);Biaxial crystal;Phase transition of optical rotation
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