Observing collisions beyond the secular approximation limit.

Quantum coherence plays an essential role in diverse natural phenomena and technological applications. The unavoidable coupling of the quantum system to an uncontrolled environment incurs dissipation that is often described using the secular approximation. Here we probe the limit of this approximation in the rotational relaxation of molecules due to thermal collisions by using the laser-kicked molecular rotor as a model system.

Effect of humidity on the absorption continua of CO and N near 4 μm: Calculations, comparisons with measurements, and consequences for atmospheric spectra.

We present a theoretical study of the effects of collisions with water vapor molecules on the absorption, around 4 μm, in both the high frequency wing of the CO ν band and the collision-induced fundamental band of N. Calculations are made for the very first time, showing that predictions based on classical molecular dynamics simulations enable, without adjustment of any parameter, very satisfactory agreement with the few available experimental determinations. This opens the route for a future study in which accurate temperature-dependent (semi-empirical) models will be built and checked through comparisons between computed and measured atmospheric spectra.

Line coupling effects in the isotropic Raman spectra of N2: a quantum calculation at room temperature.

We present quantum calculations of the relaxation matrix for the Q branch of N2 at room temperature using a recently proposed N2-N2 rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10,200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility.

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

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).

Line interference effects using a refined Robert-Bonamy formalism: the test case of the isotropic Raman spectra of autoperturbed N2.

A symmetrized version of the recently developed refined Robert-Bonamy formalism [Q. Ma, C. Boulet, and R.