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首页> 外文期刊>The Journal of Chemical Physics >Direct H-1 NMR evidence of spin-rotation coupling as a source of para -> ortho-H-2 conversion in diamagnetic solvents
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Direct H-1 NMR evidence of spin-rotation coupling as a source of para -> ortho-H-2 conversion in diamagnetic solvents

机译：直接H-1 NMR证据表明旋转旋转耦合作为硅抗磁性溶剂（官能）的对晶态转化源

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摘要

At ambient temperature, conversion from 100% enriched para-hydrogen (p-H-2; singlet state) to ortho-hydrogen (o-H-2; triplet state) leads necessarily to the thermodynamic equilibrium proportions: 75% of o-H-2 and 25% of p-H-2. When p-H-2 is dissolved in a diamagnetic organic solvent, conversion is very slow and can be considered as arising from nuclear spin relaxation phenomena. A first relaxation mechanism, specific to the singlet state and involving a combination of auto-correlation and cross correlation spectral densities, can be retained: randomly fluctuating magnetic fields due to intermolecular dipolar interactions. We demonstrate here that (i) this dipolar mechanism is not sufficient for accounting for the para -> ortho conversion rate, (ii) spin-rotation interaction, an intra-molecular mechanism, behaves similarly to random-field interaction and, thus, may be involved in the singlet relaxation rate. Also, as the para -> ortho conversion is monitored by proton nuclear magnetic resonance (NMR) of dissolved o-H-2 (p-H-2 is NMR-silent), one has to account for H-2 exchange between the liquid phase and the gas phase within the NMR tube, as well as for dissolution effects. Experimental evidence of the above statements is brought here in the case of two organic solvents: acetone-d(6) and carbon disulfide. The observed temperature dependence of the para -> ortho conversion rate shows that spin-rotation can be the dominant contribution to the p-H-2 relaxation rate in the absence of tangible dipolar interactions. Our findings shed new light on the "mysterious" mechanism of the para -> ortho conversion which has been searched for several decades. Published by AIP Publishing.
机译：在环境温度下，将100％富集的对氢（pH-2;单态）转化为邻氢（OH-2;三重态），必须对热力学平衡比例进行：75％的OH-2和25％ pH-2。当P-H-2溶解在二磁有机溶剂中时，转化率非常缓慢，并且可以被认为是由核自旋松弛现象产生的。可以保留针对单态状态并涉及自相关和交叉相关光谱密度的组合的第一松弛机制：由于分子间偶极相互作用，随机波动磁场。我们在此证明（i）（i）这种偶极机制不足以算用于估计对旁邻转换率，（ii）旋转旋转相互作用，分子内机制，与随机场相互作用类似，因此可以参与单线松弛率。此外，由于通过质子核磁共振（NMR）监测溶解OH-2（pH-2是NMR沉默）的para->邻摩转化，必须考虑液相和气体之间的H-2交换在NMR管内的相，以及溶出作用。在两种有机溶剂的情况下，在这里提出了上述陈述的实验证据：丙酮-D（6）和二硫化碳。观察到的对邻官转换率的观察到的温度依赖性表明，在没有有形双极相互作用的情况下，旋转旋转可以是对P-H-2松弛率的显性贡献。我们的调查结果阐述了帕拉的“神秘”机制的新灯 - >邻罗转换的机制已被搜查了几十年。通过AIP发布发布。

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