Molecular-based formulation of rotational diffusion coefficient and its application

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K05369
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 32010:Fundamental physical chemistry-related
• Research Institution: Niigata University
• Principal Investigator: Ohtori Norikazu 新潟大学, 自然科学系, 教授 (20272859)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 液体 / 溶液 / 回転拡散係数 / 分子動力学法 / ストークス・アインシュタイン・デバイの関係

Outline of Final Research Achievements

We have evaluated the diffusivity of translation and rotation of nitrogen molecules in pure liquid by molecular dynamics calculation to evaluate the dependence of molecular mass, moment of inertia, number density, molecular shape, filling rate, and temperature on each variable. It was formulated together with the evaluation result of the viscosity. It was found that the obtained formula can uniformly express the behavior of the diffusion coefficient and viscosity of translation and rotation at a wide range of densities and temperatures of various diatomic and triatomic molecules. It was concluded that this achieved the formulation of translational and rotational diffusivity and viscosity for linear molecules. In particular, it was clarified that the translational diffusivity and viscosity do not depend on the molecular shape, but the rotational diffusivity strongly depends on the molecular shape.

Free Research Field

基礎物理化学

Academic Significance and Societal Importance of the Research Achievements

回転拡散係数は、主として液体中での分子運動を記述する物理量として、並進運動の自己拡散係数と並んで重要な位置を占めている。一方、回転拡散に及ぼす分子形状の影響は、これまで慣性モーメントや分極などの分子内の質量や電荷の分布の影響と一体化して論じられ、純粋な形状の効果を議論した報告は皆無と言える。本研究結果は、純粋な形状の効果を、慣性モーメントや分極の効果から切り離して独立に評価し、分子形状を変数として回転拡散係数と関連するStokes-Einstein-Debyeの関係の定式化に成功した初めての成果である。