ИСТИНА

Various theoretical approaches (see e.g. [1-4]) are used in order to simulate collision- induced absorption (CIA) spectra, reliable knowledge of which is required nowadays for planetary climate modeling. Among these approaches the use of classical trajectory simulation is particularly promising since it makes possible relatively cheap evaluation of the spectral profiles using presently available ab initio calculated potential energy (PES) and induced dipole (IDS) surfaces. The goal of the current paper consists of development and numerical realization of the procedure that enables simulation of the rototranslational CIA band profile for interacting monomers of arbitrary symmetry. We start by constructing a classical intermolecular Hamiltonian in a chosen body-fixed frame. Then the equations of motion are derived along with the trajectory density function. Methods of computer algebra are used to ensure correct results. Finally extensive classical trajectory calculations are carried out to compute the resulting CIA spectrum. Markov chain technique is applied to generate a set of initial points properly distributed in the phase space. Simple anisotropic CO2-Ar prototype system was first taken as an example. The spectra for this system were considered recently in Ref. [4] using classical trajectory analysis, though the formalism in Ref. [4] is significantly at variance from our approach. Our trajectory simulation for concrete molecular pairs is supported by extensive ab initio PES and IDS calculations on a grid of angles and intermolecular separations followed by their analytical fit. [1] Frommhold, L. Collision-induced absorption in gases. Cambridge University Press, 2006. [2] Karman, T., et al. J. Chem. Phys. 2015, 142(8), 084306. [3] Hartmann, J.M., et al. J. Chem. Phys. 2011, 134(9), 094316. [4] Oparin, D., et al. J. Quant. Spectrosc. Radiat. Transfer, 2017, 196, 87.