Andrzej Witkowski

Bio: Andrzej Witkowski is an academic researcher from Jagiellonian University. The author has contributed to research in topics: Hydrogen bond & Infrared spectroscopy. The author has an hindex of 9, co-authored 13 publications receiving 727 citations. Previous affiliations of Andrzej Witkowski include American Academy of Arts and Sciences.

Infrared Spectra of H‐Bonded Systems

Abstract: For the linear triatomic X–H··· system, the separability of the X–H stretching vibrations from the hydrogen bond vibrations is analyzed in the spirit of the adiabatic approximation. The adiabatic wavefunctions for X–H stretching vibrations are shown to be suitable functions for the evaluation of the principal factors determining the infrared spectral properties of the actual species of carboxylic acid dimers and imidazole crystal. Theoretical infrared spectra in the X–H stretching region of these systems are then obtained and compared with the experimental ones. The quantitative reconstitution of the experimental spectra and, in particular, the predictions for the effect of isotopic substitution of H by D are confirmed. The principal features of the unusual spectral properties of the X–H stretching vibrations in hydrogenbonded systems seem therefore to result from a somewhat peculiar coupling mechanism suggested in the theory.

Dynamic interactions of hydrogen bonds in oxalic acid crystals

Abstract: A theoretical interpretation is presented of the IR spectra of the hydrogen bonds in three different crystalline forms of oxalic acid (α, β and dihydrate). The calculated spectra are in quantitative agreement with the experimental one for both the frequency and intensity distribution of the vibrational fine structure of the hydrogen bond absorption spectrum. The drastic changes in the IR spectra introduced by the deuterium substitution in the hydrogen bonds are quantitatively predicted by the theory.

Far‐Infrared Spectrum of the Hydrogen Bond in Acetic Acid Dimers

Abstract: An interpretation is proposed and formulated quantitatively for the explanation of the doublet structure in the far‐infrared spectrum of acetic acid dimers. The observed splitting is related to the interaction of the degenerate hydrogen bond vibrations in the dimer. Transition to the second component is allowed by the coupling with the OH stretching vibrations. Observed changes introduced in the spectrum by deuteration in the hydrogen bond confirm the proposed interpretation.

Interrelation between H-bond and Pi-electron delocalization.

Abstract: Among many various kinds of molecular interactions, the H-bond has a special position. The term is ubiquitous in the world that surrounds us, but also it is often applied in different ways. The H-bond is of great importance in natural sciences. This relates particularly to biological aspects, such as molecular recognition that could be a basis for the creation of life,1-4 formation of higher order structures of peptides and nucleic acids,5 and biochemical processes, particularly the enzymes catalyzed.6,7 One can say that the H-bond plays a double role in biological systems: on one hand, as a relatively strong directional interaction, it leads to relatively stable supramolecular structures, and on the other hand, because of dynamic features of the proton, it is an active site for initiation of chemical reactions. H-bonds are the source of specific properties of associated liquids, with water being the most popular among them.8 Water as a medium in which life was most probably created is saturated by H-bonds with highly mobile protons in between, even in the solid state.9 In many crystal lattices of organic compounds, the H-bonds are a decisive factor governing packing.10 In designing new interesting crystal structures, which is the subject of fast developing crystal engineer* To whom correspondence should be addressed. E-mail: slagra@ uni.lodz.pl or slagra@ccmsi.us. Fax: +48-42-6790447. 3513 Chem. Rev. 2005, 105, 3513−3560

Infrared Spectra of H‐Bonded Systems

Abstract: For the linear triatomic X–H··· system, the separability of the X–H stretching vibrations from the hydrogen bond vibrations is analyzed in the spirit of the adiabatic approximation. The adiabatic wavefunctions for X–H stretching vibrations are shown to be suitable functions for the evaluation of the principal factors determining the infrared spectral properties of the actual species of carboxylic acid dimers and imidazole crystal. Theoretical infrared spectra in the X–H stretching region of these systems are then obtained and compared with the experimental ones. The quantitative reconstitution of the experimental spectra and, in particular, the predictions for the effect of isotopic substitution of H by D are confirmed. The principal features of the unusual spectral properties of the X–H stretching vibrations in hydrogenbonded systems seem therefore to result from a somewhat peculiar coupling mechanism suggested in the theory.

Profiles of hydrogen stretching ir bands of molecules with hydrogen bonds: A stochastic theory. I. Weak and medium strength hydrogen bonds

Abstract: A theory is proposed to describe the shape, in inert solutions, of hydrogen stretching ir bands of complexes with hydrogen bonds. The theory uses stochastic arguments and is related to general theories of ir band profiles of liquids. The cases of weak and medium strength hydrogen bond are treated separately. In the former case the band profile is, essentially, a broad asymmetrically distorted Gaussian produced by an anharmonic coupling between the high frequency AH stretching mode and the perturbed low frequency AH⋅⋅⋅B stretching mode. In the latter case the profile is, essentially, a very broad Gaussian intersected by a number of flat or deep, broad or narrow Evans‐type transmission windows. Here, the band shaping mechanisms are the anharmonic coupling between the AH stretching and different low frequency external motions and the Fermi resonance between states involving the AH stretching and some other internal modes. Spectral manifestations of hydrogen bonded liquids represent the most extreme case of vibrational broadening and the presence of the Evans holes is its characteristic feature.