Pressure-induced variations of the intensity in the core regions of molecular absorption lines. A review

About fifteen experimental studies, carried out in the last fifty years, have evidenced that the absorber-density-normalized integrated line intensities deduced from measured absorptions in the central regions of isolated transitions of molecular gases vary with the sample pressure. Quantifying and modeling this subtle phenomenon (with pressure-induced changes typically <1 %.atm⁻¹), for which there is a recently growing interest thanks to the progress in laboratory experimental spectroscopy, raise very challenging experimental and theoretical difficulties. However this is of importance for our understanding of the underlying complex physical processes as well as for some high-accuracy demanding recent space borne remote sensing missions. In this context, we believe that a review on the subject is timely, which is proposed here by discussing the historical and current experimental and theoretical states of knowledge on this issue and its implications for the future evolution of spectroscopic databases.