从单一多位交换^(119)Sn二维交换谱求取SnCl_6^(2-)水解体系的动态交换速率常数

EVALUATION OF RATE CONSTANTS FOR SnCl_6^(2-) HYDROLYZING SYSTEM FROM A SINGLE ^(119)Sn 2D EXCHANGE SPECTRUM OF MULTI-SITE EXCHANGE

本文对如何从单一二维交换谱提取速率常数进行了理论分析,提出了一种近似处理方法,即把较短混合时间τ_m内在二维平面上磁化强度传递看成是单向进行的,进而导出了二维交换谱中所有峰强随τ_m变化的表达式。所得结果与Ernst的精确结果在一级近似下完全一致,在二级近似下略有不同,但将难以求解的问题转化成简单的代数方程、用这一方法对新近获得的SnCl_4·5H_2O在水溶液中的^(119)Sn二维交换谱进行了处理,得到与实验相吻合的结果,并求得了SnCI_6^(2-)水解体系的动态交换速率常数。

An approximation approach for evaluating rate constants from a single 2D exchange spectrum is proposed, based on theoretical analysis of the amplitude of 2D peaks. For sufficiently short mixing time tm, the magnetization transfer can be seen as single-direction-transfer from the diagonal peak to cross peak(s). The expressions of the amplitude as a function of tm are presented. The results are in agreement with that of Ernst theory within the first order approximation, but differs a little bit in the second order approximation. However, the problem has been much simplified, and the results coincide with the recently obtained 119Sn 2D exchange spectrum of SnCl62- hydrolyzing system quite well. Thus the exchange rate constants for this system are evaluated directly by the simple method.