Dipole mechanism of line broadening in amorphous solids

Abstract

Dipole–dipole interaction between molecular vibrations is the most important source of inhomogeneous line broadening in the strongest infrared absorption bands of amorphous films of N2O and O3 prepared by vapor deposition at cryogenic temperatures. This type of broadening occurs in all strongly allowed absorption bands of amorphous solids. Comparison of spectra obtained for amorphous and polycrystalline ozone show that the crystal structure is anisotropic, and most likely uniaxial. The absorption line shape of amorphous films is satisfactorily predicted by a computational model in which orientationally disordered molecules on a regular lattice interact through long-range dipole interactions. It is shown that the normal vibrations are delocalized throughout the solid, and the absorption line shape depends on the macroscopic shape and orientation of the sample.

Observation of the Berreman Effect in Infrared Reflection-Absorption Spectra of Amorphous Titanium Oxide Thin Films Deposited on Aluminum

“…It can be supposed that the asym metric tail of the LO function in the direction of low frequency has an origin similar to that obser ved in Ref. 17. However, the LO function clearly shows more than one band, and the above interpretation m ust be taken cautiously at this stage of our work.…”

Infrared spectra and band strengths of amorphous and crystalline N2O

“…Not surprisingly, the resulting N 2 O peak positions do not match those of our amorphous ice, but rather they agree well with the positions for crystalline N 2 O. (A sharp, unlabeled peak near 2260 cm 1 also suggests the crystallinity of the sample of Sivaraman et al 43 ) Finally, the single IR feature (ν 3 ) of amorphous N 2 O shown by Ovchinnikov and Wight 16,18 agrees well with the shape of that same band in our Figures 3 and 5.…”

“…[16][17][18] Among the more-recent work on solid N 2 O is that of Fulvio et al, 19 giving spectra of two fundamental and several overtone/combination bands for solid N 2 O at 16 K, along with apparent band strengths for the ν 1 (1295 cm 1 ), ν 3 (2239 cm 1 ), and 2ν 1 (2581 cm 1 ) features. Although these authors' experimental description contained many details, their spectra do not match those of Dows, 11 Yamada and Person, 12 Schettino and Salvi, 13 or Ovchinnikov and Wight, [16][17][18] and no reference was made to the phases of N 2 O ices described by, among others, Drobyshev et al 14 In the present paper, we revisit the IR spectra of N 2 O ices at 10-70 K, presenting new spectra of both the amorphous and crystalline phases along with IR band strengths. Since our experiments are motivated by possible astrochemical applications, and since the three N 2 O fundamentals are the IR features most likely to be detected by astronomical observers, we focus on those three vibrations at the expense of the weaker overtone and combination bands.…”

Berreman effect applied to phase characterization of thin films supported on metallic substrates: The case ofTiO2

“…The most likely explanation is that the crystal nature of rutile and anatase is anisotropic. In a series of papers, [38][39][40][41] Ovchinnikov and Wight investigated inhomogeneous broadening of absorption bands in the infrared spectra of both amorphous and polycrystalline sample. They have shown that the long-range dipole interactions can transcend the grain boundaries in polycrystalline samples having isotropic structures, thereby delocalizing the optical phonon modes over the entire sample and effectively eliminating the dipole broadening.…”