Abstract We have proposed the new principle of isotopic phase similarity (IPS) in the previous works I, II, of this series. The fundamental Born-Oppenheimer approximation maintains separately its applicability within each isotopic phase. The fluctuation-thermodynamic formalism is based on the developed earlier predictive model of CVL (congruent vapor-liquid) – diagram. It changes the mean-field concept of the macroscopic VLE (vapor-liquid equilibrium) – diagram to describe adequately the mesoscopic scale of volumes and time-intervals for a fluid state. The well-established by CVL-diagram fluctuation boundaries of the boil- Pb(T)- and dew-Pd(T)-pressures are important ones. They form the essential mesoscopic expansion of the single Pv(T)- vapor-pressure curve postulated by VLE- diagram. This mesoscopic peculiarity of a non-mean-field phase transition was revealed earlier for any one-component fluids. It provides the new insight into the classic theory of isotope effects. In the first instance the conventional interpretation of the vapor-pressure isotope effect (VPIE) and the molar-volume isotope effect needs an independent consideration by the comparison of CVL-diagrams for isotopes. In two previous works I, II we have introduced the undimensional fluctuation calibration complex Z o c = P 0 M / ( R T 0 ρ c ) ( P 0 = 101.325 kPa , T 0 = 1 K , M g/mol – molar mass of isotope, ρc - its critical density of mass) which provides the separation of VPIEs for the variety of isotopic families on two main types: (n) normal ( Z o c n 1 ) and (i) inverse ( Z o c i > 1 ) at low temperatures. In this work III we have applied the same IPS-methodology to the set of partially deuterated methanes CHxD4-x of i-type. The set of exclusively n-type pairs {H2O/D2O/T2O; 36Ar/40Ar; 235U/238U} was considered in works I, II. The reasonable predictive capability of IPS-principle determines systematic shifts in the critical parameters of heavier isotopes if only those for the basic lighter isotope (CH4) are known. The most impressive confirmation of IPS-principle is the reasonable concordance of its dew-pressure isotope effect (DPIE)-predictions with the experimental absolute differences between small vapor pressures of isotopes Δ P v = P v ′ − P v . We have proposed and corroborated the concept of two coupled crossover Bancroft's T b B and Clapeyron's T l g C -points. They offer the study of the difference between the vaporization enthalpies of isotopes without virial correction for non-ideality of v-phase.

中文翻译：

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同位素理论的波动方面 - III．氘代甲烷 CHxD4-x 组中的同位素相相似性

摘要 我们在本系列之前的作品 I、II 中提出了同位素相相似性 (IPS) 的新原理。基本的 Born-Oppenheimer 近似在每个同位素相中分别保持其适用性。波动热力学形式是基于 CVL（全等汽液）图的早期预测模型。它改变了宏观 VLE（汽液平衡）图的平均场概念，以充分描述流体状态的体积和时间间隔的细观尺度。由 CVL 曲线图确定的沸腾-Pb(T)-和露-Pd(T)-压力的波动边界是重要的。它们形成了由 VLE-图假定的单个 Pv(T)-蒸气压曲线的基本细观膨胀。对于任何单组分流体，非平均场相变的这种细观特性在较早时就已被揭示。它提供了对同位素效应经典理论的新见解。在第一种情况下，蒸气压同位素效应 (VPIE) 和摩尔体积同位素效应的传统解释需要通过同位素 CVL 图的比较进行独立考虑。在之前的两部作品 I、II 中，我们介绍了无量纲涨落校准复合物 Z oc = P 0 M / ( RT 0 ρ c ) ( P 0 = 101.325 kPa , T 0 = 1 K , M g/mol – 同位素摩尔质量, ρc - 其临界质量密度），它为两种主要类型的各种同位素家族提供了 VPIE 的分离：(n) 正常 (Z ocn 1 ) 和 (i) 逆 (Z oci > 1 ) 在低温下。在这项工作 III 中，我们将相同的 IPS 方法应用于 i 型部分氘化甲烷 CHxD4-x 的集合。排他性 n 型对的集合 {H2O/D2O/T2O; 36Ar/40Ar；235U/238U} 被考虑在作品 I、II 中。如果只知道基本轻同位素 (CH4) 的参数，IPS 原理的合理预测能力决定了较重同位素关键参数的系统变化。IPS 原理最令人印象深刻的确认是其露压同位素效应 (DPIE) 预测与同位素小蒸气压之间的实验绝对差异 Δ P v = P v ' - P v 的合理一致性。我们已经提出并证实了两个耦合交叉 Bancroft 的 T b B 和 Clapeyron 的 T lg C 点的概念。