J.P. Hawranek

Infrared dispersion of the pentachlorophenol–trioctylamine complex

Abstract The optical constants of the hydrogen-bonded complex of pentachlorophenol with tri- n -octylamine in binary systems were determined in the MIR range using a thin film transmission technique, which takes into account the dispersion of the refractive index in the visible region and the absorption in the NIR and MIR ranges. From these data the spectra of both components of the complex electric permittivity in the NIR and MIR regions and related high-frequency dielectric properties of the studied hydrogen-bonded complex were determined and discussed. A considerable increase of the molar vibrational polarization due to the hydrogen bond formation has been demonstrated. The vibrational polarization of the hydrogen bond exceeds the electronic polarization of this bond in the studied complex considerably. The results have been compared with data obtained previously for related systems.

Influence of Non-fundamental Modes on Mid-infrared Spectra: Anharmonic DFT Study of Aliphatic Ethers

Fundamental and non-fundamental vibrational modes, first overtones, and binary combination modes of selected aliphatic ethers (di-n-propylether, di-iso-propylether, n-butylmethyl ether, n-butylethyl ether, di-n-butyl ether, tert-buytlmethyl ether, and tert-amylmethyl ether) were modeled in a fully anharmonic generalized second-order vibrational perturbation theory (GVPT2) approach on the DFT-B2PLYP/SNST level. The modeling procedure of theoretical line shapes took into account conformational isomers of studied molecules. The calculated spectra of the above ethers were compared to the corresponding experimental spectra in the infrared (IR) region (4000-560 cm-1) of the absorption index k(ν) derived from the neat liquid thin-film transmission data. It was found that IR spectra of aliphatic ethers are heavily influenced by the bands originating from non-fundamental modes, particularly from the combination modes in the C-H stretching region (3200-2800 cm-1). Because of the effects of vibrational resonances, the intensities of overtones and combination bands originating from methyl and methylene deformation modes increase sufficiently to influence the experimental line shape in this region. Less significant contributions from non-fundamental vibrational modes were noticed in the lower IR region (1600-560 cm-1), particularly in the vicinity of the C-O stretching band. The 2700-1600 cm-1 region, which is rich in weak bands due to non-fundamental vibrations, was reproduced accurately as well. It was concluded that a fully anharmonic approach allows significantly more accurate reproduction of the complex IR line shapes, particularly in the C-H stretching region of aliphatic ethers. On the basis of the achieved agreement between the experimental and calculated spectra, it may be concluded that the anharmonic GVPT2 method can adequately reproduce the anharmonic effects and vibrational resonances in particular, influencing the IR spectra of aliphatic ethers. The results obtained in this study show that the non-fundamental modes may play a significant role in shaping the IR spectra of aliphatic ethers and similar molecules in the neat liquid phase.

Infrared dispersion of liquid sym-collidine

Abstract The optical constants of liquid sym -collidine were determined in the 12 500–600 cm −1 range using a thin film transmission technique. The complete spectrum of both components of the complex electric permittivity in the near-infrared and infrared regions and the related high-frequency dielectric properties of the liquid were determined and discussed.

The infrared dielectric function of liquid triethylamine

Abstract The spectra of both components of the complex refractive index and of the complex electric permittivity for liquid triethylamine at 298 K were estimated from thin film transmission spectra in the 3200 – 650 cm −1 range. From these data, the molar vibrational polarization was determined in selected regions, and their contribution to the total value for the studied molecule was discussed. The spectra of both components of the complex polarizability of the molecule in liquid phase were also obtained in the studied region and discussed.

Optimization of spectral band envelopes with the use of variable metric methods

Abstract A comparative study of the efficiency of 11 iterative algorithms, belonging to the class of variable metric methods was carried out, in application to the problem of optimization of spectral band envelopes. The combination of these 11 correction algorithms with 5 various 1-D minimization methods yielded an ensemble of 55 computational procedures, which were programmed in Turbo Pascal and—independently —in C++. The efficiency of the methods was tested on 33 simulated and experimental band envelopes, with the number of bands ranging from 1 to 20, amounting to 4–80 optimized band parameters. The detailed analysis of the obtained results indicates the best performance of the Goldfarb II algorithm, combined with the geometrical contraction/expansion minimization method with Goldsteins test. Very good performance is shown also by the Davidon-Fletcher-Powell method, the Broyden-Fletcher-Goldfarb-Shanno method and the unified Fletcher algorithm.

On the contour of overlapping vibrational bands in condensed phases

Abstract An approximation of the vibrational band profile in condensed phases has been developed. The entire contour is considered as a sum of overlapping components of identical shape, given by a Cauchy-Lorentz or Gauss function. The resulting functions are asymmetrical as a rule. Examples of numerical fitting of experimental vibrational bands are presented.

Infrared dispersion of the pentachlorophenol-sym-collidine complex

Abstract The optical constants of the hydrogen-bonded complex of pentachlorophenol with 2,4,6-trimethylpyridine in binary systems were determined in the 12500-600 cm −1 range using a new thin film transmission technique, which takes into account the dispersion of the refractive index in the visible region and the absorption in the NIR an MIR ranges. From these data the spectra of both components of the complex electric permittivity in the NIR and MIR regions and related high-frequency dielectric properties of the hydrogen-bonded complex were determined and discussed. A considerable increase of the molar vibrational polarization due to hydrogen bond formation has been demonstrated. The results have been compared with data obtained previously for similar systems.

Thin film FTIR transmission spectra of liquid 2,4,6-trimethylpyridine

Abstract Thin film transmission spectra of liquid sym-collidine were measured in the region 4000-500 cm−1 in cells with thicknesses in the range 3–15 μm. From these data, the spectrum of the complex refractive index was determined in this region. Forty absorption bands were detected and quantitatively described in terms of the band indices, half-widths and integrated intensities. The assignment of numerous bands is presented and discussed. The near-IR spectrum of the liquid is also reported.

Thin film transmission spectra of liquid CDCl3 in the infrared

Abstract Thin film transmission spectra of neat liquid CDCl 3 were obtained in the 3500–250 cm −1 region. From these data the spectra of both components of the complex refractive index were calculated. The imaginary part was used to calculate integrated intensities and other spectral parameters for the principal bands. The obtained results were compared with literature data and discussed.

Vibrational and reorientationl relaxation in liquid tert-butyl bromide and tert-butyl bromide-d9☆

Abstract The vibrational and reorientational correlation functions of the ν s (CBr) mode in liquid tert -butyl bromide (TBBr) and in its deuterated analogue (TBBr- d 9 ) were determined from Raman bandshapes. The Kubo product δτ m obtained by fitting the Rothschild equation to experimental data amounts to 0.36–0.45 for the studied bands, which indicates a fairly fast modulation regime in these systems. The approximation of experimental rotational correlation functions with the help of the J -diffusion model yields values of 0.11–0.12ps for the angular momentum correlation time. The second-order rotational correlation times (1.7–2.0ps) agree well with the NMR results of D.W. Aksnes, K. Ramstad and O.P. Bjorlykke, Magn. Reson. Chem., 25 (1987) 1063. Selected bandshape parameters for δ(CCC) in both compounds, ϱ(CH 3 ) in TBBr and ν s (CC) in TBBR- d 9 were also quoted.