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We investigate how dispersion analysis can profit from the use of a Lorentz-type description of the inverse dielectric function. In particular at higher angles of incidence, reflectance spectra using p -polarized light are dominated by bands from modes that have their transition moments perpendicular to the surface. Accordingly, the spectra increasingly resemble inverse dielectric functions. A corresponding description can therefore eliminate the complex dependencies of the dispersion parameters, allow their determination and facilitate a more accurate description of the optical properties of single crystals. [ABSTRACT FROM AUTHOR]

Highlights: [•] Complete dispersion analysis of polarized IR reflectance spectra was performed. [•] A technique for discriminating between anion vibrations and water librations was proposed. [•] The HOH stretching transition dipole directions were discussed. [•] The reason for the isolated ion stretching vibration red shift was discussed. [ABSTRACT FROM AUTHOR]

Polarized infrared and Raman spectra of triclinic LiAl(PO 4 )(OH) [montebrasite] single crystal were recorded for appropriate optical configurations. Dispersion analysis was applied on the infrared reflectivity spectra taken at low incidence angle (11°) to determine the oscillator parameters and the dipole directions of the polar phonons. In particular, all the 27 polar phonons, predicted by group theory for triclinic P 1 ¯ structure, were determined. The obtained dielectric tensor parameters have been checked by comparison between predicted and measured infrared spectra at higher incidence angle (34°). The azimuth and co-elevation angles obtained from the dispersion analysis showed that the response of several polar phonons is close to that of an orthorhombic system. Polarized Raman spectra obtained in several scattering geometries allowed us to obtain well-defined 24 non-polar modes, also in perfect agreement with group theory. The selection rule between Raman and infrared phonons was respected, confirming the centrosymmetric structure and ruling out any relevant influence of defects. The relatively narrow phonon bands are compatible with a highly ordered structure with fully occupied atomic sites. [ABSTRACT FROM AUTHOR]

Abstract We present the first complete dispersion analysis of the organic ethylenediamine- d -tartrate (EDDt) in single crystal form in the spectral range of 5000–100 cm−1. The obtained oscillator parameters were used to generate the polarized and the cross-polarized spectra of randomly oriented polycrystalline EDDt. The comparison of the generated with the experimental spectra confirms the value of obtained oscillator parameters and dielectric tensor function. Graphical Abstract Unlabelled Image Highlights • Only three correct dispersion analyses of organic monoclinic crystals exist by now. • First complete dispersion analysis of monoclinic organic EDDt single crystal • Verification of oscillator parameters with spectrum of polycrystalline sample [ABSTRACT FROM AUTHOR]

We developed a measurement and evaluation scheme to perform dispersion analysis on arbitrarily cut orthorhombic crystals based on the schemes developed for triclinic and uniaxial crystals. As byproduct of dispersion analysis the orientations of the crystal axes are found. In contrast to the spectra of arbitrarily cut uniaxial crystals, where the fit routine has to separate two independent principal spectra, the spectra of arbitrarily cut orthorhombic crystals are a combination of three independent spectra and the evaluation scheme gets more complex. Dispersion analysis is exemplary performed on two different crystals, which show different spectral features and different levels of difficulties to evaluate. Neodymium gallate (NdGaO 3 ) has broad overlapping reflections bands while topaz (Al 2 SiO 4 [F, OH] 2 ) has a quite high total number of infrared active bands. [ABSTRACT FROM AUTHOR]

A single crystal of neodymium gallate was investigated by FTIR-spectroscopy in the reststrahlen region between 100–1000 cm −1 . The three spectra of the crystal in principal orientations were analyzed by dispersion analysis and the dispersion parameters and the dielectric tensor function were obtained. This allows to properly characterize and quantitatively analyze films of this important substrate material by IR-optical methods. [ABSTRACT FROM AUTHOR]

We modified the measurement and evaluation scheme developed for the dispersion analysis of triclinic crystals to perform dispersion analysis of arbitrarily cut uniaxial crystals. In addition to the dispersion parameters, we determine the orientation of the optical axis and can distinguish between degenerate and non-degenerate vibrational modes. The investigated crystals comprise quartz, calcite and lithium niobate, which exhibit different levels of difficulty to evaluate the dispersion parameters and the correct orientation. [ABSTRACT FROM AUTHOR]

We present a dispersion analysis of the orthorhombic peptide single crystal Z -Aib-Aib-Aib-L-Ala-OtBu (N-benzyloxycarbonyl-α-aminoisobutyryl-α-aminoisobutyryl-α-aminoisobutyryl-L-alanine tert-butyl ester, C 27 H 42 N 4 O 7), where Z is benzyloxycarbonyl and OtBu is the tert-butylester) in the MIR spectral region by means of adapted generalized dispersion analysis, employing the naturally grown crystal faces. Based on the results we identify the orientation of the crystal axes a , b , c within the sample, and supported by a stereographic projection of the crystal, we assign the individual axes. The gained dielectric tensor function and the oscillator parameters were confirmed by forward calculation of reflection spectra of different orientations. The orientation of the crystal axes was verified by a second stereographic projection with another crystal face in the center. Unlabelled Image • First dispersion analysis of a peptide crystal. • Determination of the orientation of the molecule helices in the crystal. • Dispersion parameters confirmed by forward-calculation of different faces. • Orientation of the crystal axes and molecule helices confirmed by stereographic projection. [ABSTRACT FROM AUTHOR]