Air-water gas transfer largely influences the geochemical and biogeochemical cycles of essential atmospheric components (e.g. O₂ and CO₂), in which gas molecular diffusion in water is recognized as the rate limiting step. Isotope compositions in these gas molecules are useful tools to quantify this mass transfer process, in which diffusional isotope fractionation factors (i.e. α_diff) are the key intrinsic parameters. These α_diffs are often determined by gas transfer experiments with large uncertainties because the roughness of water surface can affect the interpretation of experimental data. In this study, molecular dynamic simulations were employed to investigate directly the diffusional isotope fractionation for singly and doubly substituted isotopologues of H₂, N₂, and O₂. The results show that diffusional isotope fractionation factors are dependent on both the molecular mass and moment of inertia, which is consistent with previous findings for polyatomic molecules rather than for monoatomic ones. When comparing with the kinetic isotope fractionation (i.e. α_k) determined by gas transfer experiments, I found that α_k is likely close to (α_diff)^1/2 within errors (i.e. α_k= (α_diff)^1/2), rather than to (α_diff)^2/3 that has often been employed to calculate α_diff using α_k in literature (i.e. α_k= (α_diff)^2/3). If this is the case, the results further indicate that the nuclear quantum effect is not significant when α_diff is of interest. With these findings, I determined the isotope fractionation relationship θ for different O₂ isotopologues to be 0.5100±0.0002 and 1.9535±0.0013 respectively for ¹⁷θ_diff (≡ln¹⁷α_diff/ln¹⁸α_diff) and ³⁶θ_diff (≡ln³⁶α_diff/ln¹⁸α_diff) as an example.

_{空气-水气体转移很大程度上影响了基本大气成分（例如O 2}和CO ₂ ）的地球化学和生物地球化学循环，其中气体分子在水中的扩散被认为是限速步骤。这些气体分子中的同位素组成是量化这种传质过程的有用工具，其中扩散同位素分馏因子（即 α _diff）是关键的内在参数。这些 α_差异s 通常由具有较大不确定性的气体转移实验确定，因为水面的粗糙度会影响实验数据的解释。在这项研究中，分子动力学模拟用于直接研究 H ₂、N ₂和 O ₂的单取代和双取代同位素体的扩散同位素分馏。结果表明，扩散同位素分馏因子取决于分子质量和惯性矩，这与先前对多原子分子而非单原子分子的发现一致。与气体转移实验确定的动力学同位素分馏（即α _k）相比，我发现α _k在误差范围内可能接近 (α _diff ) ^{1/2 （即 α} _k = (α _diff ) ^1/2），而不是经常用于使用 α _k in计算 α _{diff的 (α diff} ) ^2/3文献（即α _k = (α _diff ) ^2/3）。_{如果是这种情况，则结果进一步表明，当关注 α diff}时，核量子效应并不显着。根据这些发现，我确定不同 O ₂同位素体的同位素分馏关系 θ分别为 0.5100±0.0002 和 1.9535±0.0013^以17 θ _diff (≡ln ¹⁷ α _diff /ln ¹⁸ α _diff ) 和³⁶ θ _diff (≡ln ³⁶ α _diff /ln ¹⁸ α _diff ) 为例。