Isolated line shapes of molecular oxygen: Requantized classical molecular dynamics calculations versus measurements

Abstract

We present comparisons between measured isolated line shapes of molecular oxygen in air at various pressures and those calculated, free of any adjusted parameter, using requantized classical molecular dynamics simulations (rCMDS). The measurements have been made for the R1Q2, P9P9, P11P11, P13P13, and P15Q14 transitions in the O 2 singlet-band [a 1 g ← X 3 − g (0,0)] by the frequency-stabilized cavity ring-down spectroscopy technique. This work extends a previous study made for a single oxygen line [Phys. Rev. A 87, 032510 (2013)] and confirms the quality of this theoretical approach over broad ranges of pressure and rotational quantum number. Indeed, not only the collisional broadening coefficients but also the (small) deviations of observed line shapes with respect to the Voigt profile are accurately predicted. These results illustrate the viability of using the rCMDS method as a benchmark for the development and testing of simpler parametrized line profiles that are suitable for the analysis of underlying physical mechanisms and for atmospheric remote sensing applications.

Molecular dynamic simulations of N2-broadened methane line shapes and comparison with experiments

“…[14][15][16][17][18][19] From reliable intermolecular potentials, the evolution of a system involving a large number of molecules can be computed, including the time dependence of the position of the center of mass, of the translational and angular velocities, and of the orientation of each molecule. The auto-correlation function of the molecular dipole moment can be also computed.…”

“…Specifically, the measured spectral shapes and their evolution with pressure are satisfactorily reproduced by the calculations. [14][15][16][17][18][19] Classical molecular dynamic simulations (CMDSs) were also successfully applied to non-linear molecules as for the case of pure H 2 O 20,21 and H 2 O diluted in N 2 . 22 In these situations, quaternion coordinates were used to treat the rotation of the molecules.…”

Spectral shapes of Ar-broadened HCl lines in the fundamental band by classical molecular dynamics simulations and comparison with experiments

“…[19][20][21][22] For that, all measured and calculated spectra have been fitted with Voigt profiles, and we then compare the obtained fit residuals and retrieved parameters. This allows another comparison between measured and calculated spectra.…”

“…Comparison between CMDS-calculated spectra and measurements for both CO 2 and O 2 absorption lines at different pressures and in various spectral regions showed very good agreement. [19][20][21][22] In the present work, CMDS are thus used for the calculation of the absorption line shapes of HCl diluted in Ar. For that, a new requantization procedure has been adopted in order to represent the rotational motion of HCl molecules.…”

“…In recent years, classical molecular dynamics simulations (CMDS) have been successfully used to predict the line shapes of linear molecules such as CO 2 or O 2 without use of any adjustable parameter. [19][20][21][22] From reliable intermolecular potentials, one can calculate the auto-correlation function of the dipole moment and then the absorption spectrum. Using a requantization procedure for the classical molecular rotation, the spectrum of a line can be calculated and then compared with the measured profile.…”