多环芳烃Lennard-Jones系数理论研究

Theoretical Calculations of Lennard-Jones Parameters of Polycyclic Aromatics Hydrocarbons

针对多环芳烃分子与氦气间的Lennard-Jones(L-J)系数及二元扩散系数进行了理论计算,重点分析了两种对分子间势能场进行各向同性近似的方法的适用性和准确性.研究发现对于两个维度尺寸接近的多环芳烃平面分子,先对势能场进行球形平均再计算L-J系数的传统方法,相比于新近文献中提到的一维优化方法,计算结果与实验值、经验估计值更为接近;而对于分子量基本相同但形状相差较大的不同分子,不同计算方法得到的结果差别较大.理论计算结果在低温下与现有的经验预测模型结果保持了较好的一致性;而理论计算方法相比于经验预测方法,更能体现出分子结构差异对L-J系数及二元扩散系数的影响.

Lennard-Jones（L-J）parameters and binary diffusion coefficients of polycyclic aromatic hydrocarbons（PAHs）interacting with bath gas helium were computed theoretically.The applicability and accuracy of two different methods for averaging anisotropic intermolecular potentials were discussed.In the first method,the intermolecular potentials were spherically averaged first and then used to determine the L-J parameters,while in the second method,the L-J parameters were obtained on the basis of one-dimensional minimization averaged over the relative orientations of interacting partners.The results suggested that,for planar PAH of similar sizes,binary coefficients computed using the first approach are closer to the experimental measurements and empirical predictions than those using the second method.For planar PAH having similar molecular mass but different shapes,different methods give quite different results.The theoretical results agree well with the empirical model predictions at low temperatures,and effect of the molecular structure on the L-J parameters or binary diffusion coefficients can be revealed better by the theoretical calculations than by the empirical predictions,especially at high temperatures.