Benedict Jason B, Coppens Philip
Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260-3000, USA.
J Phys Chem A. 2009 Apr 2;113(13):3116-20. doi: 10.1021/jp809170t.
The quadratic dependence of the rate of photodimerization of alpha-trans-cinnamic acid induced by 532 nm pulsed laser light confirms a two-photon mechanism in the single crystals. Single crystals in well-defined orientations and circularly polarized light were used in the experiments. The reaction rate deviates from first-order kinetics, but fits the JMAK expression with a coefficient indicating a mechanism intermediate between a random distribution of product molecules in the crystal and the existence of growing nuclei. The reaction is accompanied by a large change in the monoclinic beta-angle of the unit cell, corresponding to increased pi-overlap between adjacent molecules and therefore to an increased reaction rate. The improved penetration of the light in the crystal and more homogeneous product formation are significant advantages in studies of mechanisms of chemical reactions in single crystals.
532nm脉冲激光诱导的α-反式肉桂酸光二聚化速率的二次方依赖性证实了单晶中的双光子机制。实验中使用了具有明确取向的单晶和圆偏振光。反应速率偏离一级动力学，但符合JMAK表达式，其系数表明产物分子在晶体中的分布介于随机分布和存在生长核之间的一种机制。该反应伴随着单斜晶胞β角的大幅变化，这对应于相邻分子间π-重叠的增加，从而导致反应速率增加。光在晶体中更好的穿透以及更均匀的产物形成是单晶化学反应机制研究中的显著优势。
