Line mixing effects in isotropic Raman spectra of pure N2: A classical trajectory study

Abstract

Line mixing effects in the Q branch of pure N2 isotropic Raman scattering are studied at room temperature using a classical trajectory method. It is the first study using an extended modified version of Gordon's classical theory of impact broadening and shift of rovibrational lines. The whole relaxation matrix is calculated using an exact 3D classical trajectory method for binary collisions of rigid N2 molecules employing the most up-to-date intermolecular potential energy surface (PES). A simple symmetrizing procedure is employed to improve off-diagonal cross-sections to make them obeying exactly the principle of detailed balance. The adequacy of the results is confirmed by the sum rule. The comparison is made with available experimental data as well as with benchmark fully quantum close coupling [F. Thibault, C. Boulet, and Q. Ma, J. Chem. Phys. 140, 044303 (2014)] and refined semi-classical Robert-Bonamy [C. Boulet, Q. Ma, and F. Thibault, J. Chem. Phys. 140, 084310 (2014)] results. All calculations (classical, quantum, and semi-classical) were made using the same PES. The agreement between classical and quantum relaxation matrices is excellent, opening the way to the analysis of more complex molecular systems.

Recent advances in collisional effects on spectra of molecular gases and their practical consequences

“…3.3.3) but also of the off-diagonal elements of the relaxation matrix. This possibility has been used recently for predictions of LM effects in isotropic Raman spectra of pure N 2 [237]. For this system, good agreement was obtained ( Fig.…”

“…A series of papers [193][194][195][196][234][235][236][237][238] has resurrected the purely classical approach proposed by R.G. Gordon fifty years ago [239,240].…”

“…13: Computed relaxation-matrix elements W(j'←j=6) between the Q(6) lines and various Q(j') for N 2 -N 2 at 298 K. CC/CS denote the quantum results from [229], cRB the corrected-RB predictions from [228] and C3D(db) the results of classical calculations. After [237].…”

Room temperature self- and H2-broadened line parameters of carbon monoxide in the first overtone band: Theoretical and revised experimental results

“…This method is simple, visual, and computationally efficient. This classical approach, with applications to a variety of molecular systems [41][42][43][44][45][46][47][48][49][50][51][52][53],…”

Line mixing in parallel and perpendicular bands of CO2: A further test of the refined Robert-Bonamy formalism

“…5,6 Fully quantum calculations become unfeasible for more complex systems due to large numbers of coupled channels involved. With the recent exception of the classical approach of S. Ivanov and co-workers, 7 most of the previous line mixing studies were based on semi-empirical fitting or scaling laws, such as the energy corrected sudden (ECS) model widely used in simulations of atmospheric spectra. 1,8,9 On the other hand, based on classical collisional paths and intermolecular potentials for molecular systems of interest, semi-classical approaches to calculate the relaxation matrix such as that developed by Cherkasov 10 have existed for years.…”