ИСТИНА

Classical trajectory (CT) approach has recently proved itself [1,2] to be fairly competitive against purely quantum [3] or molecular dynamics [4] methods in the simulation of collision-induced absorption (CIA) band profile. The list of molecular pairs, the CIA spectra of which were studied based on the classical trajectories, is however extremely limited up-to-now. It includes only complexes of CO2 with rare gases and N2-N2 system. That is why there is a need to extend the application of this powerful method to a variety of molecular partners having more degrees of freedom and possessing different potential and induced dipole relief. We present results of the rototranslational CIA band simulation for two weakly interacting CO2 molecules using our developed CT technique. Salient features of the latter can be reduced to the following. First, assuming collisions of rigid monomers, the exact classical equations of motion were derived using generalized internal coordinates and the body-fixed frame. Second, potential energy and induced dipole were computed on the grid of intermolecular coordinates using CCSD(T) ab initio method. Afterwards, the potential and dipole surfaces were represented as smooth functions. Third, initial conditions for scattering trajectories were properly sampled using the Markov chain Monte Carlo procedure. Fourth, classical trajectories starting from the fixed large initial distance were propagated using SUNDIALS differential equation solver [5]. Finally, classical spectral profiles were obtained from the averaging of the squared Fourier transform of the dipole moment temporal evolution. These spectra were then desymmetrised to account for quantum nature of molecular system’s interaction with electro-magnetic field. Following the comparison of our obtained spectra with available experimental and previously calculated data we comment on the accuracy of the CT method against other approaches, as well as on the possible contribution to the calculated spectral profile from true bound dimers, which are currently yet disregarded in the frame of our approach. This work was partially supported by RFBR and RFBR-CNRS Grants in the frame of 18-05-00119, 18-32-20156, 18-55-16006 projects. References: 1. D.V. Oparin, N.N. Filippov, I.M. Grigoriev, A.P. Kouzov, JQSRT, 196, 87-93 (2017). 2. D.N. Chistikov, A.A. Finenko, Y.N. Kalugina, S.E. Lokshtanov, S.V. Petrov, A.A. Vigasin, Classical trajectory simulation of collision-induced absorption spectra, 25th International Conference on High Resolution Molecular Spectroscopy Bilbao, Spain, September 3rd – 7th, 2018. 3. T. Karman, "Collision-induced absorption by oxygen and nitrogen molecules" PhD dissertation, Nijmegen, 2018. 4. B. Bussery-Honvault and J-M. Hartmann, J. Chem. Phys. 140 (5), 054309 (2014). 5. A.C. Hindmarsh, P.N. Brown, K.E. Grant, S.L. Lee, R. Serban, D.E. Shumaker, and C.S. Woodward, ACM Transactions on Mathematical Software, 31(3), pp. 363-396, 2005.