Collision-induced infrared spectra

A. Borysow and L. Frommhold. Collision-induced infrared spectra of H2-He pairs at temperatures from 18 to 7,000 K Overtone and hot bands. Astrophys. J., 341 549, 1989. 

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... 

This is the highest molecular weight compound for which infrared multiphoton dissociation has been observed in our laboratories to date. A similar pathway was indicated by the collision-induced dissociation spectrum of this ion. Limited CID experiments were performed on some of the other laser-desorbed ions discussed here and in general the CID and PD pathways were the same. 

Infrared Spectroscopy. The infrared spectroscopy of adsorbates has been studied for many years, especially for chemisorbed species (see Section XVIII-2C). In the case of physisorption, where the molecule remains intact, one is interested in how the molecular symmetry is altered on adsorption. Perhaps the conceptually simplest case is that of H2 on NaCl(lOO). Being homo-polar, Ha by itself has no allowed vibrational absorption (except for some weak collision-induced transitions) but when adsorbed, the reduced symmetry allows a vibrational spectrum to be observed. Fig. XVII-16 shows the infrared spectrum at 30 K for various degrees of monolayer coverage [96] (the adsorption is Langmuirian with half-coverage at about 10 atm). The bands labeled sf are for transitions of H2 on a smooth face and are from the 7 = 0 and J = 1 rotational states Q /fR) is assigned as a combination band. The bands labeled... 

Spectroscopy is concerned with the interaction of light with matter. This monograph deals with collision-induced absorption of radiation in gases, especially in the infrared region of the spectrum. Contrary to the more familiar molecular spectroscopy which has been treated in a number of well-known volumes, this monograph focuses on the supermolecular spectra observable in dense gases it is the first monograph on the subject. 

Fig. 3.19. The far infrared absorbance spectrum (in arbitrary units) of pure HD at 43 amagat and 77 K (smoothed). The sharp Ro(J) lines sit upon a broad collision-induced background after [398],...

Fig. 7.3. Upper figure Emission spectrum of Jupiter in the far infrared two diffuse, dark fringes are seen at the H2 Sb(0) and Sb(l) rotational transition frequencies, caused by collision-induced absorption in the upper, cool regions. The lower figure presents an enlarged portion which shows the dimer structures near the So(0) transition frequency [150].

D. Levesque, J. J. Weis, Ph. Marteau, J. Obriot, and F. Fondere. Collision induced far infrared spectrum of liquid N2 Computer simulations and experiment. Molec. Phys., 54 1161, 1985. 

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. ... 

Moon and Oxtoby presented a general theory for collision-induced absorption, which occurs in the near- and far-infrared region of the spectrum, in molecules. Speeific results were presented for the case of symmetric linear Dooh) and tetrahedral (Tj) molecules. The authors subsequently applied their nonasymptotic theory of the pair dipole moment to the eal-culation of binary spectral integrals and the far-infrared speetrum for dinitrogen.The authors also evaluate the eontributions to the seeond-order multipole model (including the anisotropy of the polarizability, the hexadecapole moment and the dipole-oetopole polarizability). 

Collision-induced absorption from free pairs of molecules appear as broad lines or bands located at the wavenumbers of the pure-rotation or vibration-rotation transitions in the participating individual molecules. Figure 3.3.6 shows the spectrum for H2-H2 collisions (Bachet et al., 1983) [see also Courtin (1988)]. In the far infrared (below 200 cm ) a weak translational band is also present. In H2 the prominent features in planetary atmospheres occur at the pure-rotation / = 0 -> 2 and 1 3 transitions located at 354 and 587 cm . The widths of collision-induced features are extremely large, about 100 cm or more, because the time during the collision in which the partners are interacting is very short ( 10 seconds or less). The width of a spectral line is related to the reciprocal of the collision duration. 

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