Line Lists Including Intensities for Diatomic Molecules of Astronomical Interest and Remote Sensing Measurements of Greenhouse Gases

Line lists including positions and absolute intensities have been produced using a combination of theoretical and experimental methods, for several spectroscopic systems of diatomic molecules, including the C2 and 12C13C Swan systems, the CN, 13CN, and C15N A2Π-X2Σ+ (red), B2Σ+-X2Σ+ (violet), and X2Σ+ state rovibrational systems, the CP A2Π-X2Σ+ system, and the NH X3Σ− state rovibrational and rotational transitions. Preliminary calculations for the OH X2Π state rovibrational transitions have also been performed. RKR potential energy curves, vibrational wavefunctions, and matrix elements (MEs) were calculated using the programs RKR1 and LEVEL. The MEs were transformed from Hund’s case (b) to (a), for which an equation was derived. Einstein A values were calculated from the case (a) MEs and molecular constants using PGOPHER. These lists will be useful in the fields of astronomy, combustion science, materials science, and anywhere else that transitions of these diatomic molecules are investigated. Line intensities have also been used to retrieve an atmospheric CO2 volume mixing ratio. A new technique for the satellite remote sensing of atmospheric greenhouse gases via absorption of short-wave infrared laser signals transmitted between counter-rotating satellites in low Earth orbit has recently been proposed; this would enable the acquisition of a long-term, stable, global set of altitude-resolved concentration measurements. The first ground-based experimental demonstration of this new infrared-laser occultation method is presented, in which the atmospheric absorption of CO2 near 2.1 µm and CH4 near 2.3 µm were measured over a 144 km path length between two peaks in the Canary Islands, using relatively low power diode lasers. The retrieved CO2 volume mixing ratio of 400 ppm (±15 ppm) is consistent within experimental uncertainty with simultaneously recorded validation measurements. The new method has a sound basis for monitoring atmospheric CO2 and other greenhouse gases