Journal of Colloid and Interface Science ( IF 9.4 ) Pub Date : 2022-09-24 , DOI: 10.1016/j.jcis.2022.09.021 Sruthy Poulose 1 , M Venkatesan 1 , Matthias Möbius 1 , J M D Coey 1
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Hypothesis
Ortho and para water are the two nuclear isomers where the hydrogen protons align to give a total nuclear spin of 1 or 0. The equilibrium ratio of 3:1 is established slowly in freshly evaporated water vapour while the isomers behave distinct gasses, with their own partial pressures. Magnetic-field-induced ortho ⟷ para transformations are expected to alter the evaporation rate.
Experiment
Evaporation from beakers of deionized water and a 6 M solution of urea is monitored simultaneously for periods from 1 to 60 h with and without a 500 mT magnetic field, while logging the ambient temperature and humidity. Balances with the two beakers are shielded in the same Perspex container. Many runs have been conducted over a two-year period.
Findings
The evaporation rate of water is found to increase by 12 ± 7% of in the field but that of water with dissolved urea decreases by 28 ± 6%. Two effects are at play. One is dephasing of the Larmor precession of adjacent protons on a water molecule in a field gradient, which tends to equalize the isomer populations. The other is Lorentz stress on the moving charge dipole, which can increase the proportion of the ortho isomer. From analysis of the time and field dependence of the evaporation, we infer that the ortho fraction is 39 ± 1% in fresh vapour from water and 60 ± 5% in fresh vapour from urea.
中文翻译：
水和尿素溶液在磁场中的蒸发;核异构体的作用
假设
邻位水和对位水是两种核异构体，其中氢质子排列以产生 1 或 0 的总核自旋。在新蒸发的水蒸气中缓慢建立 3：1 的平衡比，而异构体则表现为不同的气体，具有自己的分压。磁场诱导的邻位 ⟷ 对位变换预计会改变蒸发速率。
实验
在有和没有 500 mT 磁场的情况下，同时监测去离子水和 6 M 尿素溶液烧杯的蒸发量 1 至 60 小时，同时记录环境温度和湿度。带有两个烧杯的天平被屏蔽在同一个有机玻璃容器中。在两年的时间里已经进行了多次运行。
发现
发现田间水的蒸发率增加了 12 ± 7%，但含有溶解尿素的水的蒸发率降低了 28 ± 6%。有两个影响在起作用。一种是水分子上相邻质子的 Larmor 岁差在场梯度中的去相，这往往会使异构体群相等。另一个是移动电荷偶极子上的洛伦兹应力，它可以增加邻位异构体的比例。通过分析蒸发的时间和场依赖性，我们推断水新鲜蒸气中的正位分数为 39 ± 1%，尿素中的新鲜蒸气为 60 ± 5%。
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