The local dynamics of polyetherimides: Conformational probes, IR Fourier transform spectra, and quantum-chemical calculations

The IR Fourier transform absorption spectra were used to study the rotational mobility of macromolecule fragments (local dynamics) of several vitreous polyetherimides by the method of conformational probes. The temperatures of the freezing of conformational equilibria of probes were determined. The IR spectra of diphenyl ether, 2,2-diphenylpropane, phthalimide, and N-phthalimide were studied; these molecules were used as models of fragments of monomeric units of polyetherimides. Quantum-chemical calculations of the energies and vibrational spectra of these molecules were performed by the B3LYP method with the 6–31G(d,p) basis set. The rotational mobility of benzene rings in the main chain of polyetherimide macromolecules was estimated, and the nature of secondary relaxation transitions was determined. The IR spectra of polyetherimides were interpreted. The rotational mobility of the CH₃ and CF₃ groups of polyetherimides was estimated from the temperature dependence of absorption band contours of these groups.     

IR spectra of water clusters with captured ethane molecules: Computer simulation

Uptake of ethane molecules by a monodisperse aqueous system was simulated by molecular dynamics. The cluster (H₂O)₂₀ characterizing the system remains stable until the number of the captured C₂H₆ molecules becomes larger than four. Addition of ethane molecules to the disperse aqueous system decreases both the real and imaginary parts of the dielectric permittivity in the frequency range 0 ≤ ω ≤ 1000 cm^?1. The integral IR absorption coefficient of the disperse system containing C₂H₆ molecules increases, and the frequency-average reflection coefficient decreases. The continuous reflection spectra transform into band spectra. The heat-radiating power of the clusters decreases upon absorption of ethane molecules. The cluster that took up two ethane molecules exhibits the highest radiating power. This cluster has the largest number of active electrons interacting with the arriving wave.     

First-principle calculations ofK-edge X-ray absorption spectra for small iron and nickel clusters

In this study we present theoretical X-ray absorption near-edge spectra (XANES) evaluated for Fe₂, Ni₂, and Ni₃ using a modified multiple-scattered wave procedure. The calculations were performed for different internuclear distances of the dimers and by varying the geometry from linear to equilateral triangular for Ni₃. The calculated absorption spectra for both Fe₂ and Ni₂ predict a broad resonant structure at the threshold and weak 1s transitions to unoccupied valence orbitals ?5→0 eV giving a shoulder at the threshold. The resonance structure at the threshold of Ni₃ appeared to be sensitive to the geometry of the clusters.     

The IR spectra of the products of the reaction of gallium atoms with iodine molecules in solid argon

The IR spectra of the reaction of gallium atoms with iodine molecules from the argon matrix are studied. Most of the bands observed have been assigned to stretching vibrations in tri-, di-, and monoiodide. Both the intensity relationship and the semiempirical estimates indicate that the valence angle should be no more than 110° in gallium di-iodide.     

IR spectroscopic andab initio quantum-chemical study of the products of hydrolysis of silicon tetrafluoride at low water concentrations

According to the results of IR spectroscopic study and quantum-chemical calculations, hydroxo derivatives SiF_4-x(OH)_x are formed in the course of hydrolysis of silicon tetrafluoride in the presence of small amount of water along with hexafluorodisiloxane. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 92–96, January, 1999.     

Electronic spectra of metal cluster molecules

The electronic absorption spectra (UV-visible-NIR) of a range of molecular metal cluster compounds, including new spectra of Pt₃₀₉(phen*)₃₆O₂₈ in solution and Au₅₅(PPh₃)₁₂Cl₆ in the solid state, are discussed and compared with the spectra of colloidal particles of the corresponding metals. We consider frontier orbital separations, the development of interband absorptions, the possible appearance of molecular plasma resonances, and charge-transfer in the solid state.     

Interactions of small nickel clusters with methane molecules

The matrix IR spectra of the Ni _n + CH₄ system have been studied, and quantum-chemical calculations of the Ni-CH₄, Ni₂-CH₄, and Ni₃-CH₄ complexes have been carried out. The Ni₂-CH₄ complex is characterized by long Ni-H and Ni-C distances. For Ni₃ complexes, these distances are much shorter and the global energy minimum corresponds to the H-Ni₃-CH₃ structure. In this structure, one of the hydrogen atoms is completely eliminated from methane and goes to the middle of the Ni-Ni bond, forming a trigonal HNi₂ < fragment. Based on the calculation, the transition barrier of the Ni-CH₄ complex in H-Ni-CH₃ was evaluated (8 kcal/mol).     

The characteristic IR spectra of heterothiometallic cluster compounds

This article summarizes and presents the obtainable characteristic IR spectra of the existing heterothiometallic cluster compounds containing the [MXS₃]²⁻ (X=O, S; M=V, Mo, W, Re) moiety. The MS stretching vibration modes are classified into four categories including ν(MS_t), ν(Mμ₂-S), ν(Mμ₃-S) and ν(Mμ₄-S) according to the different conjunction ways between the transition metal and sulfur atoms. The structures of the heterothiometallic cluster compounds could be inferred from their characteristic IR spectra, the core structure's symmetry of the heterothiometallic clusters and the M/M′ ratio.     

Ab initio quantum-chemical calculations of interactions of ions and hydrides of alkali metals with C3H6 and C4H8 molecules

Calculations of the C₃H₆ · LiH, C₄H₈ · M⁺, and C₄H₈ · MH systems and of C₂H₂ · MH complexes (M = Li or Na) were carried out by the unrestricted Hartree-Fock-Roothaan (UHF) method with partial optimization of the geometry using fixed geometric parameters of the C₃H₆ and C₄H₈ molecules. The standard 3-21G and 6-31G* basis sets were used. Unlike the C₃H₆ · LiH structure, the C₄H₈ · M⁺ and C₄H₈ · MH systems are typical complexes. It was found that the C₄H₈ · M⁺, C₄H₈ · MH, and C₂H₂ · MH complexes are similar in coordination of M⁺ ions and MH molecules by carbon atoms in spite of considerable differences in the interatomic distances (–1 A) between these atoms in the C₄H₈ and C₂H₂ molecules. The heats of formation (Q), which were calculated in the UHF/6-31G* approximation and using second- and fourth-order Möller-Plesset perturbation theory taking into account the electron correlation energy in the MP2/6-31G*. MP4(SDQ)/6-31G*, and MP4(SDTQ)/6-31G* approximations, satisfy the following relationships: Q(C₂H₃ · MH) < Q(C₄H₈ · MH) < Q(C₄H₈ · M⁺). It was observed that in going from Li to Na the corresponding values of Q tend to decrease.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 7, pp. 1636–1640, July, 1996.     

Characteristics of the complexing of chitosan with sodium dodecyl sulfate,according to IR spectroscopy data and quantum-chemical calculations

The complexing of protonated chitosan with dodecyl sulfate ions in water solutions is studied using IR spectroscopy data and quantum-chemical calculations. It is established that the electrostatic interaction between the protonated amino groups of chitosan and dodecyl sulfate ions is apparent in the IR spectrum as a band at 833 cm^?1. The need to consider the effect the solvent has on the formation of hydrogen-bound ion pairs [CTS⁺ ? C₁₂H₂₅O₃^-] is shown via a quantum-chemical simulation of the equilibrium geometry and the energy characteristics of complexing and hydration.     

IR absorption spectra and association of acridinium salts with hydrogen halide molecules

It was observed that the reaction of acridine with hydrogen halides under heterogeneous conditions proceeds in two steps: An acridinium salt is formed in the first step, while a complex of the salt with hydrogen halide molecules is formed in the second step. The formation of a complex leads to substantial changes in the region of the stretching vibrations of NH⁺ bonds, and this makes it possible to propose the direct participation of these bonds in complexing. The band of the stretching vibrations of NH⁺ bonds of the acridinium ion has a complex structure that changes markedly as a function of the sort of halogen ion and replacement of hydrogen by deuterium and in the case of complexing with the hydrogen halide. It is proposed that the structure of this band is due to Fermi resonance.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 99–101, January, 1981.     

Interaction of O+ ion with water molecules: A quantum-chemical study

The interaction of O⁺ ion with several (from one to four) water molecules was studied by theab initio (UMP4/4-31G^*) and semiempirical (AM1) quantum-chemical methods. It was found that the energy of binding the O⁺ ion to the first water molecule is appreciably higher than those of binding to the subsequent water molecules. In the complex with a water molecule, whose structure corresponds to that of water oxide, the O⁺ ion retains high reactivity. The barrier to the transfer of O⁺ ion to another water molecule is much lower than the barrier to analogous transfer of O atom from the molecule of water oxide, despite the lower dissociation energy of the H₂O−O bond. Consideration of subsequent interactions with water molecules leads to an increase in the barrier to the transfer of O⁺ ion. The doublet and quadruplet excited states of the O⁺+2 H₂O system were also studied. In these cases, the formation energies are well described by the ion-dipole model. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 981–988, June, 2000.