Spectra rotovibrational

Isotope spectra. Rotovibrational spectra of deuterium, and of deuterium-rare gas mixtures, have also been recorded over a wide range of temperatures and densities [342]. The differences between the H2-X and D2-X spectra (with X = H2 or D2, respectively, or a rare gas atom) are much like what has been seen above for the rototranslational spectra. 

Fig. 0.2. (a) The comb spectrum of N2 considered as a quantum rotator. The envelope of the rotational structure of the Q-branch slightly split by the rotovibra-tional interaction is shaded, (b) The depolarized rotovibrational spectrum of N2 at corpuscular density n = 92 amagat, T = 296 K and pressure p = 100 atm. The central peak, reported in a reduced (x30) scale is due to a polarized component [5] (V) experimental (—) best fit. 

Fig. 1.1. Induced rotovibrational absorption of O2 pairs. The heavy curve represents the measurement the light curve is a theoretical envelope ( stick spectrum ) of the Raman 0 and S branches. The envelope of the Q branch is shown as a broken line after [128].

Other systems consisting of molecules other than H2 have similar rotovibrational spectra. However, the various rotational lines cannot usually be resolved, owing to the smallness of the rotational constants B and the typically very diffuse induced lines. One example, the spectrum of compressed oxygen, was shown above, Fig. 1.1. It consists basically of three branches, the Q, S, and O branch. The latter two are fairly well modeled by the envelope of the rotational stick spectra, similar to that shown in Fig. 3.20, but shifted by the fundamental vibration frequency. 

Hydrogen-Helium Mixtures. Accurate ab initio dipole surfaces for both the rototranslational collision-induced absorption spectrum in the far infrared [280], and the rotovibrational collision-induced absorption spectrum in the near infrared [151], have been obtained that could have... 

H2 He He rotovibrational band. The density dependence of the H2-He enhancement spectrum in the fundamental band of hydrogen has been measured previously, using a trace of hydrogen in helium of thousands of amagats [121, 175, 142] ternary moments were measured at room temperature. The measurements suggest again greater values of the spectral moments, Table 6.7. 

The significance of collision-induced absorption for the planetary sciences is well established (Chapter 7) reviews and updates appeared in recent years [115, 165, 166, 169-173]. Numerous efforts are known to model experimental and theoretical spectra of the various hydrogen bands for the astrophysical applications [170, 174-181]. More recently, important applications of colhsional absorption in astrophysics were discovered in the cool and extremely dense stellar atmospheres of white dwarf stars [14, 43, 182-184], at temperatures from roughly 3000 to 6000 K. Under such conditions, large populations of vibra-tionally excited H2 molecules exist and collision-induced absorption extends well into the visible region of the spectrum and beyond. Numerous hot bands, high H2 overtone bands, and H2 rotovibrational sum and difference spectral bands due to simultaneous transitions that were never measured in the laboratory must be expected. Ab initio calculations of the collisional absorption processes in the dense atmospheres of such stars have yet to be provided so that the actual stellar emission spectra may be obtained more accurately than presently known. 

We note that in the infrared region of the spectrum, another collision-induced spectroscopy is well known that in the laboratory is usually observed in absorption. CILS is related to collision-induced absorption as ordinary Raman spectroscopy is related to the usual rotovibrational spectroscopy in the infrared. An extensive bibliography and a recent update of the literature concerning collision-induced absorption have been compiled previously. ... 

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