Infrared Spectroscopy of Symmetric and Spherical Top Molecules for Space Observation, Volume 2

1IR Spectra in Space Observation

The IR (infrared) range corresponds to the frequency band between 10⁴ GHz and 5 × 10⁵ GHz, therefore to wavelengths ranging between 0.78 µm and 1,000 µm. According to the ISO system (ISO 20473, 2007), this range is divided into three regions corresponding to near IR from 780 nm to 3,000 nm (sunlight), mid-IR from 3 μm to 50 μm (thermal source) and far IR from 50 μm to 1,000 μm (source in astronomy). For a given electronic state, the interaction between an electromagnetic wave in this range and a physical system in gas, liquid, solid or possibly plasma state is reflected by a transition between two vibrational and/or rotational energy states of the system, which are discrete and/or in the continuum. The possible physico-chemical processes, such as the absorption and emission of photons, elastic (Rayleigh) scattering and inelastic (Raman, Compton) scattering, dissociation, ionization and various possible combinations and interferences of these phenomena can be observed using optical instruments, such as spectrometers or telescopes. These instruments can operate on site in a laboratory or from an observatory or in the space (aboard a space probe). Depending on the latter sites and the system under observation, various options should be considered for the successful completion of an observation process.

1.1. Introduction

In a laboratory, experimental IR spectroscopy of atmospheric molecules is mainly studied in the gas phase.

Taking into account ...