NMR波谱学中的高温近似的有效性及其相关问题

高温近似(HTA)是NMR波谱学和MRI技术中久经考虑且应用最广的一个近似. 最近几年有一大批引人注目的文章断言对高场下的浓溶液，如水的质子COSY谱，该近似会 失效. 与声称的HTA失效同样令人惊讶的是其副产品之一，即认为在低粘度液体如水里，存 在分子间的多量子相干(MQC). 根据理论分析及实验结果，本文将对液体中HTA和分子间MQC 作一仔细考查. 结论是：(1)室温下，常规NMR样品如水，不是一个宏观量子系统；(2)室温下，HTA仍然是NMR里最值得信赖的近似；(3)质子COSY谱(如水)中所观察到的多重自旋回波( MSE)峰并不意味存在分子间的量子力学自旋相互作用.

THE VALIDITY OF HIGH TEMPERATURE APPROXIMATION IN NMR SPECTROSCOPY AND ITS RELATED PROBLEMS

A large body of conspicuous publications in recent years asserts that the high temperature approximation (HTA), a mostly tested and most widely used assumption in NMR spectroscopy and MRI technology, is invalid for concentrated samples in high magnetic fields such as for a proton COSY spectrum of water. A by product of the alleged collapse of HTA, which is equally surprising, is the existence of intermolecular multi quantum coherences (MQC) in low viscosity liquids such as water. In this work, both HTA and intermolecular MQCs in liquids will be critically examined in light of our theoretical analysis and experimental results. Our conclusions are: (1) There are no macroscopic quantum systems in conventional NMR samples such as water at room temperature. (2) At room temperature, high temperature approximation is still one of the most trustworthy approximations applicable to NMR and (3) The MQCs observed in proton COSY spectrum in, e.g., water, have nothing to do with quantum mechanical intermolecular spin interactions.