Julien Lamouroux

Molecular dynamics simulations for CO2 spectra. IV. Collisional line-mixing in infrared and Raman bands

Ab initio calculations of the shapes of pure CO2 infrared and Raman bands under (pressure) conditions for which line-mixing effects are important have been performed using requantized classical molecular dynamics simulations. This approach provides the autocorrelation functions of the dipole vector and isotropic polarizability whose Fourier-Laplace transforms yield the corresponding spectra. For that, the classical equations of dynamics are solved for each molecule among several millions treated as linear rigid rotors and interacting through an anisotropic intermolecular potential. Two of the approximations used in the previous studies have been corrected, allowing the consideration of line-mixing effects without use of any adjusted parameters. The comparisons between calculated and experimental spectra under various conditions of pressure and temperature demonstrate the quality of the theoretical model. This opens promising perspectives for first principle ab initio predictions of line-mixing effects in absorption and scattering spectra of various systems involving linear molecules.

The Importance of Trajectory Models in Complex Robert‐Bonamy Formalism Calculations : Application to the Rotational Band of H2O Broadened by N2, O2, and Air

In a recent study by R. Gamache and A. Laraia [1], the semiclassical Complex Robert‐Bonamy (CRB) formalism was used to calculate the half‐widths for the rotation band transitions of H216O broadened by N2, O2 and air. The Robert‐Bonamy model of approximate trajectories (parabolic) derived from the isotropic intermolecular potential was used. In this work, the importance of considering realistic dynamics model is demonstrated by the comparison of the half‐widths obtained in [1] and new calculations using the (more realistic) Hamilton’s Equations model. The comparisons of this work with the previous one clearly demonstrate differences larger than the uncertainties desired by the spectroscopic and remote sensing communities.In a recent study by R. Gamache and A. Laraia [1], the semiclassical Complex Robert‐Bonamy (CRB) formalism was used to calculate the half‐widths for the rotation band transitions of H216O broadened by N2, O2 and air. The Robert‐Bonamy model of approximate trajectories (parabolic) derived from the isotropic intermolecular potential was used. In this work, the importance of considering realistic dynamics model is demonstrated by the comparison of the half‐widths obtained in [1] and new calculations using the (more realistic) Hamilton’s Equations model. The comparisons of this work with the previous one clearly demonstrate differences larger than the uncertainties desired by the spectroscopic and remote sensing communities.

On the Way to Complex Robert‐Bonamy Calculations of Self‐, Nitrogen, Oxygen, and Air‐Broadened Line Shape Parameters of CO2

Calculations of the pressure‐broadened half‐width and pressure‐induced line shift are made for CO2 with N2, O2, air, and CO2 as the buffer gas. It will be shown that the intermolecular potential for these systems is unusually simple, which has lead to many problems and complications in the calculations. Comparison with measurements of both the half‐width and line shift will be shown and the future direction of the work presented.