中文摘要：

从同位素分馏的气-液相界面特征的视角出发，分析自然条件下水面蒸发和降水冷凝的同位素分馏过程存在的差异，分析表明降水氘剩余值产生的直接原因为水面蒸发过程与降水冷凝过程分别遵循动力学分馏与平衡分馏原理，而界面效应是决定蒸发-冷凝过程会否受到动力学过程影响的内因。水面蒸发过程的比界面面积较小，界面效应较大，水分子扩散作用显著，因此，自然条件下水面蒸发过程需要考虑水分子扩散的动力学过程，属于非平衡分馏；相反，降水冷凝过程的比界面面积巨大，界面效应影响很小，分馏基本不受分子扩散分馏影响，降水冷凝过程符合平衡分馏原理。用以上结论作为假设条件，模拟10~40℃从海水蒸发到降水冷凝的水循环过程，模拟结果与全球降水线相吻合，佐证了造成降水氘剩余产生的内在原因为水面蒸发过程与降水冷凝过程的界面效应不同的结论。

英文摘要：

Study on the characteristic of hydrogen and oxygen isotopes in precipitation is an important aspect of water cycle research. However, the production process of deuterium excess （D-excess） in rain water has not been fully ex- plained. From the perspective of characteristics of air-liquid interface, the differences in isotopic fractionation between the processes of free water evaporation and rain water condensation are analyzed. The result shows that the two proces- ses follow the kinetic fractionation and the equilibrium fractionation, respectively. This directly indicates the genera- tion of D-excess in rain water, however, the interface effect of evaporation-condensation processes controls whether the diffusion process controls the fractionation or not. The free water evaporation process under natural conditions has a smaller specific interface area, the interface effect of isotopic fraetionation is large, and the molecule diffusion is ap- parent. Thus, the free water evaporation is a non-equilibrium fractionation process; on the other hand, the process of rain water condensation has a larger specific interface area, the interface effect is ignorable, and the molecule diffu- sion does not affect the isotopic fractionation. This process is characterized as the equilibrium fractionation. Using the above result as the assumed conditions, the isotopic fractionation process of water cycle from seawater evaporation to precipitation condensation is simulated under different temperature conditions （10 -40℃ ）. The simulated result and the Global Meteoric Water Line （GMWL） coincide with each other, which supports the conclusion that the difference of the interface effects in the free water evaporation and the rain water condensation processes causes the D-excess in precipitation.