Chapter I - Introduction

Abstract

We here introduce, by using atmospheric observations from several instruments, the various manifestations of the effects of pressure on the spectra of gases that are discussed in the following chapters of Collisional Effects on Molecular Spectra. We first illustrate the pressure broadening of spectrally and collisionally isolated lines (of CH4) by using transmissions recorded by a solar-occultation satellite borne spectrometer. The emission collected from a balloon around a Q branch of CO2 with closely spaced transitions then introduces the line-mixing process where intensity is transferred among the overlapping pressure-broadened lines. Limb observations from space, with recordings of the transmission for various tangent heights in the region of the intense 4.3 µm CO2 band are used, in a third step, to demonstrate the potential importance of the far wings. Finally, ground-based solar occultation measurements clearly evidence the significant collision-induced absorption by O2 near 1.27 µm.