The spectrum of CO2 in the photographic infrared has been studied with absorbing paths up to 5500 m. Thirteen absorption bands were found of which eleven have been analyzed in detail. One of these is due to C13O2. From the band origins of the C12O2 bands improved values for some of the anharmonic constants of the molecule have been derived.
The study of the rotational structure of the photographic infrared CO2 bands has yielded considerably improved values for the rotational constants. The new values are B000=0.39020 cm-1, α1=+0.00109, α2= -0.00073, α3=+0.00307 cm-1. From these the following equilibrium values of rotational constant, moment of inertia, and internuclear distance are obtained: Be=0.39155 cm-1, Ie=71.468×10-40 gm cm2, re=1.16005×10-8 cm. By taking account of the effect of Fermi resonance, excellent agreement of the observed B[υ] values with those calculated from the αi and Be is obtained.
The l-type doubling in the states 0110, 1113, and 0313 has been determined. The agreement of the splitting constants q with those obtained from theory is satisfactory.
G. HERZBERG and L. HERZBERG, "Rotation-Vibration Spectra of Diatomic and Simple Polyatomic Molecules with Long Absorbing Paths," J. Opt. Soc. Am. 43, 1037-1044 (1953)