Peer-reviewed publications
- 1. Journal of Chemical Physics, 2026
1. Density dependence of measured line intensities for O2 transitions
2026
Project partners CNRS-LMD and CNRS-LIPhy, together with project collaborator NIST, published a new article in the Journal of Chemical Physics.
For the first time, line intensity depletion effect with increasing gas density is reported for O2 transitions. This effect, attributed to the finite duration of collisions, alters the line-shape of the transitions by redistributing a portion of the intensity from a relatively narrow spectrum, described by an impact-approximation-based profile, to a broad pedestal with a width that is inversely related to the collision duration. Using classical molecular dynamic simulations (CMDS), we predicted details regarding this mechanism for O2 with four collision-partners: O2, N2, Ar and He at a temperature of 296 K. These simulations were validated by comparisons with experimental intensity depletion coefficients obtained from absorption spectra of the 1.27 µm band of O2 in air, Ar and He recorded using high-precision cavity ring-down spectroscopy (CRDS) spectrometers at NIST (United States of America) and LIPhy (France). For air-broadened O2, more specifically, a mean depletion value of ~0.3 % amagat-1 was observed with almost no resolvable rotational dependence. The temperature dependence of the intensity depletion in this system was also investigated by CMDS suggesting a nearly temperature dependence. Finally, simulations of atmospheric solar absorption spectra were implemented to quantify the impact of neglecting this depletion effect on the retrieved surface pressure, resulting in a negatively biased measurement of ~0.14 % with a spread of ~0.02 % caused by seasonal variations in gas temperature.
Tran et al. J. Chem. Phys. 164, 014305 (2026); doi: 10.1063/5.0302649