Matrix Isolation Vibrational Spectroscopy Research Articles

A hydrogen-bonded CH2F2⋯CO complex: ab initio and matrix isolation study

The structure and spectroscopy of hydrogen-bonded complexes of partially fluorinated methanes attract considerable interest from both fundamental and applied points of view. Here we report an experimental and theoretical study on CH2F2⋯CO complex, which represents the first example of difluoromethane complex characterized by matrix isolation vibrational spectroscopy. According to the computations at the CCSD(T)/CBS (MP2/CBS) level of theory with ZPVE correction, the interaction energy of the most stable structure is 0.78 (0.84) kcal/mol. The calculated complexation-induced shifts for this structure are in reasonable agreement with experiment. The complex exhibits characteristic blue shifts of the C–H stretching modes (by 3.8 and 10.4 cm−1 for symmetrical and antisymmetrical vibrations, respectively) and red shifts of the C–F stretching modes (by −0.8 and −4.2 cm−1 for symmetrical and antisymmetrical vibrations, respectively); the C–O stretching is blue-shifted (+5.4 cm−1). The comparison of new complex with previously known species of this kind is discussed.

Studies of intermolecular interactions by matrix isolation vibrational spectroscopy: self-association of ammonia

Infrared and Raman spectra are reported for ammonia trapped in argon and nitrogen matrices over a range of concentrations. Infrared spectra are also reported for mixtures of ammonia and trimethylamine trapped in argon matrices. The results are discussed in relation to previous infrared studies. The experimental data demonstrate that the ammonia dimer contains one molecule acting as an electron acceptor and the other as an electron donor, i.e. it has an open chain structure of the type H 3N⋯HNH 2 (though not necessarily the classical linear structure). The hydrogen bonding interaction in the dimer is very weak, suggesting that the structure of the dimer in the matrix may be similar to that found in the gas phase. The data available for the ammonia trimer in matrices do not provide unequivocal evidence for either a cyclic or open chain structure; the symmetric cyclic structure appears to give the best fit to the observed spectra.

ChemInform Abstract: Molecular Complexes of Hydrogen Halides with Ethers and Sulphides Studied by Matrix Isolation Vibrational Spectroscopy

Abstract Infrared spectra are reported for mixtures of dimethyl ether, diethyl ether, hydrogen sulphide, dimethylsulphide and diethylsulphide with hydrogen chloride or hydrogen bromide in argon or nitrogen matrices. In addition to the bands due to the 1:1 complexes, absorptions due to 1:2 and 2:1 complexes were identified in many of the mixtures. The position and band shape of the perturbed HX stretching absorptions of the 1:1 complexes are discussed.

Molecular complexes of hydrogen halides with ethers and sulphides studied by matrix isolation vibrational spectroscopy

Infrared spectra are reported for mixtures of dimethyl ether, diethyl ether, hydrogen sulphide, dimethylsulphide and diethylsulphide with hydrogen chloride or hydrogen bromide in argon or nitrogen matrices. In addition to the bands due to the 1:1 complexes, absorptions due to 1:2 and 2:1 complexes were identified in many of the mixtures. The position and band shape of the perturbed HX stretching absorptions of the 1:1 complexes are discussed.

Strongly hydrogen-bonded molecular complexes studied by matrix isolation vibrational spectroscopy. Part 4.—Dimethyl sulphoxide–hydrogen halide complexes

Infrared spectra are reported of strongly hydrogen-bonded complexes between dimethyl sulphoxide or [2H6]dimethyl sulphoxide and hydrogen chloride or hydrogen bromide in argon and nitrogen matrices. Although there are differences between the spectra of the complexes in the two matrices, the extent of proton transfer does not change markedly from an argon matrix to a nitrogen matrix (unlike the amine–hydrogen halide complexes). There is substantial mixing of the O⋯H⋯Cl stretching and bending modes with vibrational modes of the dimethyl sulphoxide molecule. In the hydrogen bromide complex, the proton is more or less equally shared between the oxygen and bromine atoms; the extent of proton transfer is smaller in the hydrogen chloride complex.

Strongly hydrogen-bonded molecular complexes studied by matrix isolation vibrational spectroscopy. Part 3.—Ammonia–hydrogen bromide and amine–hydrogen bromide complexes

Infrared spectra are reported of strongly hydrogen-bonded complexes between ammonia or amines (methylamine, dimethylamine and trimethyl-amine) and hydrogen bromide trapped in argon and nitrogen matrices. There are substantial differences between the spectra of the complexes in the two matrices, which are attributed to increased proton transfer from hydrogen bromide to the amine in the more polar nitrogen matrix. The extent of proton transfer increases from ammonia–hydrogen bromide in an argon matrix (where the proton is shared more or less equally between the nitrogen and bromine atoms) to trimethylamine–hydrogen bromide in a nitrogen matrix (where the proton is almost completely transferred to the amine).

Hydrogen sulphide – halogen complexes studied by matrix isolation vibrational spectroscopy

Infrared spectra are reported of mixtures of hydrogen sulphide with chlorine or bromine in low-temperature argon or nitrogen matrices. The H2S … Cl2 and H2S … Br2 complexes were identified from the perturbed halogen stretching vibration. Absorptions due to the corresponding hydrogen halides provided evidence that reaction was occurring between the hydrogen sulphide and halogen (despite the use of a twin-jet deposition), and other reaction products were tentatively identified from the observed absorptions.

Matrix isolation vibrational spectroscopy as a tool for studying conformational isomerism

The use of matrix isolation vibrational spectroscopy to study conformational isomerism is described. Methods of distinguishing conformational splitting from matrix splitting are discussed. Examples are given of molecules for which the conformational equilibrium existing in the gas phase prior to deposition is trapped out in the matrix, of molecules which exhibit reversible interconversion of conformers at matrix temperatures, and of a molecule for which the conformational distribution trapped out in the matrix is strongly dependent on matrix polarity. Results obtained for molecules which exhibit infrared-induced isomerisation in matrices are discussed.

Nucleic acid bases studied by matrix isolation vibrational spectroscopy: Uracil and deuterated uracils

A vibrational assignment of the isolated uracil molecule is presented, based on i.r. and Raman spectra of uracil trapped in argon and nitrogen matrices and i.r. spectra of seven deuterated derivatives of uracil isolated in argon matrices. The observed spectra agree well with previous quantum mechanical calculations. The relationships observed between the monomer bands, bands due to associated uracil in argon matrices and the spectrum of the pure solid lead to a revised vibrational assignment for uracil in the solid phase. As well as large shifts in the NH stretching and out-of-plane bending modes between the monomer and the hydrogen-bonded solid, many other bands show appreciable shifts as a consequence of the extensive mixing of the NH in-plane bending modes with the CH in-plane bending and ring stretching modes. The spectrum of the associated uracil species in matrices suggests that it is a cyclic dimer, linked by C 2O … HN 1 hydrogen bonds.

Strongly hydrogen-bonded molecular complexes studied by matrix-isolation vibrational spectroscopy. Part 2.—Amine–hydrogen chloride complexes

Infrared spectra are reported of a strongly hydrogen-bonded complex between ammonia and hydrogen chloride trapped in argon and nitrogen matrices. There are substantial differences between the spectra of the complex in the two matrices, and these are attributed to increased proton transfer from hydrogen chloride to ammonia in the more polar nitrogen matrix. The corresponding gas-phase complex would be expected to display less proton transfer than the complex in an argon matrix.

Strongly hydrogen-bonded molecular complexes studied by matrix-isolation vibrational spectroscopy. Part 1.—The ammonia–hydrogen chloride complex

Infrared spectra are reported of a strongly hydrogen-bonded complex between ammonia and hydrogen chloride trapped in argon and nitrogen matrices. There are substantial differences between the spectra of the complex in the two matrices, and these are attributed to increased proton transfer from hydrogen chloride to ammonia in the more polar nitrogen matrix. The corresponding gas-phase complex would be expected to display less proton transfer than the complex in an argon matrix.

Molecular complexes of cyclopropane with hydrogen halides and water studied by matrix-isolation vibrational spectroscopy

Infrared spectra of cyclopropane-hydrogen halide and cyclopropane-water complexes show similar perturbations of the cyclopropane modes, suggesting that all have the proton donor “hydrogen-bonded” to the ring edge. The spectrum of the cyclopropane-water complex is consistent with water forming a bifurcated hydrogen bond to the ring.

Analytical Applications of Matrix Isolation Fourier Transform Infrared Spectroscopy

A review of analytical applications of matrix isolation Fourier transform infrared spectroscopy is presented. The characteristics of matrix isolation spectroscopy are discussed along with practical techniques for obtaining analytically useful results. A few studies relating to matrix isolation used in conjunction with Raman and conventional IR spectroscopy are reviewed. The majority of analytical applications of matrix isolation vibrational spectroscopy has entailed the use of FT-IR techniques. Qualitative and quantitative results from a number of sample types are presented. The coupling of matrix isolation vibrational spectroscopy with chromatographic separations is reviewed.

Alkene‐halogen complexes studied by matrix isolation vibrational spectroscopy

AbstractVibrational spectra of mixtures of chlorine, bromine or iodine with ethene or 2,3‐dimethylbut‐2‐ene (tetramethyl‐ethene) in low‐temperature argon or nitrogen matrices are reported. The shifts observed for the halogen and CC stretching modes of the 1:1 alkene‐halogen complexes are related to the structure of the complexes.

Studies of intermolecular interactions by matrix isolation vibrational spectroscopy: Self-association of water

The mid- and far-infrared spectra of water in argon and nitrogen matrices have been reinvestigated. The water molecule rotates in an argon matrix, but in a nitrogen matrix two low-frequency bands are attributed to libration of the water monomer about its A and C rotational axes. Combinations of these modes with the stretching and bending modes of the water monomer were observed. A detailed concentration-dependence study enabled bands to be attributed to dimer, trimer, and tetramer or higher multimers. The dimer and trimer were both found to have open chain structures, whereas tetramer or higher multimer species appear to be predominantly cyclic. Intermolecular modes, observed for dimer and trimer in the far-infrared spectra, are tentatively assigned.

Study of intermolecular interactions by matrix isolation vibrational spectroscopy

The application of matrix isolation infrared and Raman spectroscopy to the study of the self-association of hydrogen bonding substances is discussed. The use of the technique to elucidate the structures of small multiner species of hydrogen chloride, hydrogen cyanide, water and ammonia is described. The results of far infrared spectral studies enable some of the hydrogen bond stretching and bending modes of these species to be identified. Matrix spectra of the pyridine-hydrogen chloride complex are also discussed.

Studies of intermolecular interactions by matrix isolation vibrational spectroscopy and normal coordinate analysis: Self-association of hydrogen cyanide

A detailed study of the infrared spectra of hydrogen and deuterium cyanide in noble gas, nitrogen and carbon monoxide matrices at 4 K and 20 K has enabled the bands observed to be assigned to monomer, dimer, trimer, tetramer and higher multimer species. Force constants calculated for the linear dimer are used to predict the spectrum of the trimer. The nature of the trapping sites occupied by the monomer and linear dimer, and the structure and trapping site of a second type of dimer observed only in argon matrices, are discussed.

Studies of intermolecular interactions by matrix isolation vibrational spectroscopy

Matrix isolation infrared and Raman spectroscopy can be used to study both the self-association of hydrogen bonding substances and hetero-association i.e. the formation of molecular complexes. The techniques used and the range of interaction which can be examined are illustrated by reference to studies of the self-association of hydrogen cyanide and ammonia, molecular complexes between hydrogen chloride and a range of molecules, and molecular complexes between alkenes and halogens.

Studies of Intermolecular Interactions by Matrix Isolation Vibrational Spectroscopy

Studies of Intermolecular Interactions by Matrix Isolation Vibrational Spectroscopy