多环芳烃Lennard-Jones系数理论研究

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.