Rev. Phys. Appl. (Paris) 16, 49-66 (1981)
DOI: 10.1051/rphysap:0198100160204900

A study of infrared radiation of vibrationally excited CO in the 4.7 μm band and CO2 in the 4.3 μm and 2.7 μm bands

N.N. Kudryavtsev et S.S. Novikov

Moscow Institute of Chemical Physics, U.S.S.R. Academy of Sciences, Moscow, 117977, U.S.S.R.

Abstract
A method is discussed suitable for the calculation of the spectral and integrated, over vibrational-rotational bands, radiation and absorption characteristics of diatomic and linear triatomic molecules in the absence of thermodynamic equilibrium between the vibrational and translational degrees of freedom. Radiation intensity I and black width εof CO2 molecules in the 4.3 μm and 2.7 μm bands, and CO molecules in the 4.7 μm band with a significantly excited degrees of freedom typical of molecular lasers have been calculated. By finding the logarithmic derivatives of the radiation intensity and black width of a band it has been shown to what degree I and ε depend on pressure, optical path length and vibrational temperatures. It is demonstrated that the strongest effect on the radiation intensity of the vibrationally nonequilibrated molecular gas is exerted by the vibrational temperatures of the active (emitting) modes in a given band. This ensures a high accuracy and reliability in determining the vibrational temperatures of the thermodynamically nonequilibrated gas from the measurements of the IR-radiation intensity. It is shown with particular reference to a CO2 molecule that simultaneous measurements of the radiation intensity in the two vibrational-rotational bands, at 4.3 μm and 2.7 μm, make it possible to unequivocally find the vibrational temperatures of asymmetric stretching as well as combination modes of this molecule.

Résumé
L'étude théorique de l'émission et de l'absorption IR des gaz moléculaires a été réalisée dans les conditions qui sont caractéristiques pour le résonateur d'un laser à gaz. On a étudié les composantes typiques des milieux laser : l'oxyde de carbone (bande 4,7 p) et gaz carbonique (bandes 4,3 μ et 2,7 μ). Pour ces deux bandes vibrations-rotations on a effectué le calcul numérique des valeurs d'intensité et d'émissivité spectrales et intégrales (pour la bande correspondante) ainsi que des dérivées logarithmiques de l'intensité intégrale par rapport à la pression et aux températures de translation et de vibration. Les intervalles de changement des paramètres étudiés sont les suivants : pour la température de vibration : T vib = 600-2 200 K, pour les températures de rotation et de translation Trot, T = 100-1 100 K, pour la pression P = 10-4-10 atm., pour l'épaisseur optique X = 10-4-10 atm.cm.

PACS
0130R - Reviews and tutorial papers: resource letters.
3310G - Vibrational analysis molecular spectra.
3310J - Vibrational rotational analysis molecular spectra.
3320E - Infrared molecular spectra.

Key words
carbon compounds -- infrared spectra of diatomic inorganic molecules -- infrared spectra of polyatomic inorganic molecules -- molecular rotation vibration calculations -- molecular vibration calculations -- reviews -- infrared radiation -- vibrationally excited CO -- absorption characteristics -- linear triatomic molecule -- translational degrees of freedom -- black width -- CO sub 2 molecules -- excited degrees of freedom -- molecular lasers -- radiation intensity -- pressure -- optical path length -- vibrational temperature -- vibrational rotational band -- asymmetric stretching -- combination modes -- vibrational degree of freedom -- IR radiation