B. Jordanov

FT-IR linear dichroic solute spectra of nematic solutions as a tool for IR band assignment

Abstract FT-IR polarization spectra of diphenylacethylene (tolane), pyrene and maleic anhydride, dissolved and oriented in a nematic liquid crystal mixture, were recorded and processed by means of the Thulstrup—Eggers procedure of stepwise reduction. The IR active vibrations could be unequivocally assigned to their symmetry classes on the basis of their band polarizations. Some peculiarities were observed for the polarizations of a few spectral bands.

Reduced IR-LD spectra of substances oriented as nematic solutions

Abstract Applications of linear dichroic (LD) IR spectra, processed according to the “stepwise reduction” method of Thulstrup and Eggers[1], are shown in this article for the purposes of IR band assignment. Several typical examples visualizing the possible cases are demonstrated.

Vibrational assignment of benzophenone and some of its isotopic species in the solid phase

Abstract Vibrational spectra of benzophenone- d 03 - d 5 - d 10 and - 18 O in the solid phase have been measured in the Raman (4000–20 cm −1 ) and infrared (4000–100 cm −1 . Their differential infrared linear dichroin spectra of oriented polycrystalline layers (4000– 400 cm −1 ) have been also recorded and studied. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes. The presence of syn and anti -phase vibrations of both phenyl rings is rediscussed. The previous assignments of the in-plane deformation of the carbonyl group and of the fundamentals below 300 cm −1 are questioned and corrected.

FTIR linear dichroic spectra of substances dissolved and oriented in a nematic liquid crystal

Abstract Some opportunities for studying linear dichroic FTIR spectra of molecules dissolved and oriented in a nematic liquid crystal of very poor IR spectrum (Merck ZLI-1538) are presented. The method allows one to obtain in a simple manner direct information about the symmetry properties of the IR transitions of the dissolved molecules. Some suitable examples are given.

Total Reflection Prisms as Achromatic IR Retarders

Retarders based on total internal reflections are discussed. Quarterwave retardation can be obtained by a single reflection when one is using material of high refractive index (≥2.4), as it is available for the IR range. Alternatively, the influence of the beam divergence can be efficiently compensated for. Several optical designs and first results are presented.

Vibrational polarization spectroscopy of fluorene: alignment in stretched polymers and nematic liquid crystals ☆

New linear dichroism spectra in the mid-IR region of fluorene aligned in stretched polymers and nematic liquid crystals are compared with earlier experimental and theoretical investigations. Linear dichroism spectra of molecules aligned in such anisotropic solvents are simple to obtain, especially for small and medium sized molecules. Most molecules obtain a satisfactory alignment by these methods and the spectra are simple to interpret. The information obtained from these spectra about vibrational transition moment directions is often crucial for vibrational assignments in molecules like fluorene. Even high quality calculations are still unable to provide safe assignments for all fundamentals in fluorene as long as they are only compared with traditional spectra. Linear dichroism spectra provide a separation of the experimental information according to symmetry classes (particularly striking for molecules of C 2v and similar symmetries); this reduces the assignment puzzle drastically. In the present case the result is an almost complete and safe assignment of all symmetry allowed invibrational fundamentals of fluorene. A number of earlier assignments, which had been questioned or were doubtful, have been confirmed or corrected.q 1999 Elsevier Science B.V. All rights reserved.

The physical solution of the inverse vibrational problem: I. A perturbation treatment

Abstract An attempt, based on perturbation theory, is made to distinguish the correct physical solution from the infinite number of possibilities for the inverse vibrational problem.

Study of overlapped bands by means of reduced IR linear dichroic spectra

Abstract Overlapping of bands and accidental degeneracy often occur in the vibrational spectra of large molecules. One frequently finds in the literature, particularly on vibrational analysis of aromatic compounds, one and the same frequency for vibrations belonging to different symmetry classes without any clear experimental evidence for such an assignment. Reduced linear dichroic IR spectra open in principle the opportunity for checking such situations.

POLARIZED FT-IR SPECTRA OF TRANS-STILBENE, TOLANE, PYRENE AND PHENAZINE ORIENTED IN A NEMATIC SOLVENT

Abstract FT-IR polarization spectra of trans -stilbene, tolane, pyrene and phenazine dissolved and oriented in the nematic liquid crystal ZLI-1538 (Merck) were studied with respect to their applicability for symmetry assignment of the IR bands. Obtaining knowledge on the orientation state of the solute must procede the use of the polarization spectra for this purpose since unusual orientations might sometimes take place. The pyrene molecules, for example, turn out to be oriented along an axis nearly crossing over their carbon atoms 3 and 10 while other molecules studied are ordered along their long axes. A correction of some assignments was done.

Acrylonitr1le anion-radical detection by infrared internal reflection spectra

Abstract The application of internal reflection spectroscopy to the study of interface boundary layers has been extended over cases in which unstable particles appear at the interface as a result of imposing a negative electrical potential on the germanium hemicylinder, used simultaneously as an optical prism in the internal reflection spectroscopic device and as an electrode. The appearance of the particles is detected by their internal reflection spectrum. The method has been applied in the case of the electrochemically induced polymerization of acrylonitrile. Two particles were found to be generated during electrolysis. They are assigned to the anionradical and to the di-anion of acrylonitrile.