Zofia Mielke

Anharmonicity and hydrogen bonding: I. A near-infrared study of methanol trapped in nitrogen and argon matrices

Abstract The infrared spectra of six isotopic species of methanol trapped in solid nitrogen and argon were measured in the domain 7300–300 cm−1. Among the various combinations and overtones observed, the 2ν1 (OH or OD stretching), 2ν6 (OH or OD bending) and ν1+ν6 transitions were examined as a function of the concentration and compared to the ν1 and ν6 fundamentals. Most of the bands of monomer and dimer were identified. For aggregates larger than the dimer no absorption assignable to 2ν1 was detected, which, taking into account the accuracy of the intensity measurements, leads to a ν1/2ν1 intensity ratio greater than 1000 for these polymers, to be compared to ≈20 for the monomer and 400 for the proton donor molecule of the dimer. An opposite situation is encountered for the bending mode, the ν6/2ν6 intensity ratio decreasing from monomer to polymers, possibly because of a Fermi resonance between 2ν6 and ν1 whose frequencies get closer in case of aggregation. For the ν1+ν6 combination the effects of hydrogen bonding are not as dramatic as in the case of the overtones. From the frequencies and relative intensities some anharmonicity parameters were deduced. Noticeable differences between the spectra of the proton donor and of the proton acceptor molecules of the dimer are explained by changes in the dipole moment function upon H-bond formation.

Photolysis of isothiocyanic acid HNCS in low-temperature matrices. Infrared detection of HSCN and HSNC isomers

Abstract A combination of matrix isolation technique and Fourier transform infrared spectroscopy has been used to study the low-temperature photochemistry of isothiocyanic acid HNCS. Near UV photolysis with a medium-pressure mercury lamp of the matrix isolated HNCS/DNCS precursor in nitrogen and argon led to the formation of two unobserved, so far, isomers: thiocyanic acid HSCN and isothiofulminic acid HSNC and their deuterated analogs. Both species are formed as primary products presumably via two reaction channels: formation of the [H⋯NCS] and hydrogen migration leading to the HSCN molecule and formation of the [HNC⋯S] followed by rearrangement to HSCN and HSNC species.

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.

Far-infrared spectra of benzoic acid

Abstract Crystalline benzoic acid has been studied by far-infrared spectroscopy in the spectral region of 20–230 cm −1 with a view to a determination and an assignment of the pure lattice and the intermonomer vibrations. An anomalous behaviour, similar to the one found earlier in the mid-IR, is observed for the asymmetric OH…O stretching band with regard to the number of components of the band and its changes as a function of temperature and deuteration. The experiments were carried out for single crystals of fully hydrogenated benzoic acid (− h 6 ) with polarization analysis, and for powder of h 6 , d 1 , d 5 and d 6 benzoic acid at temperatures between 6 and 295 K. An explanation of these anomalies is proposed.

Matrix reactions of P2 and O3 molecules

Abstract Matrix reactions of P 2 and isotopic ozone molecules have been studied using both heated GaP and discharge of P 4 as sources of P 2 . Isotopic shifts and multiplets support identification of PO, PO 2 , P 2 O, P 2 O 2 , P 2 O 3 , P 2 O 4 , P 2 O 5 and PO 2 − in these experiments.

Far IR spectra of acetic acids in the gas phase. A reinvestigation of the intermonomer vibrations

Abstract As part of our programme on the dimers of carboxylic acids, we report here results from the far infrared spectra in the 20–230 cm −1 region for the four isotopically substituted species of acetic acid dimers (CH 3 COOH) 2 , (CH 3 COOD) 2 , (CD 3 COOH) 2 , (CD 3 COOD) 2 . These more confident and in parts entirely new experimental data permit us to assign the third IR active low-frequency vibration that was missing up to now. In good agreement with earlier predictions, this mode has been observed at 56 cm −1 for the totally hydrogenated dimer. Furthermore, on these new quantitative spectra the isotopic ratios of the band positions of the intermonomer vibrations are checked against those of the moments of inertia for the H-bond (or D-bond) samples separately. The comparison of the intensities of the FIR absorption bands allows us to postulate a slight but specific difference between an OH⋯O and OD⋯O bond. For the complex band centred at 171 cm −1 we propose an analysis of the band shape by Fermi resonance interactions.

Photolysis of the OC⋯HONO complex in low temperature matrices: Infrared detection and ab initio calculations of nitrosoformic acid, HOC(O)NO

Photochemistry of OC⋯HONO complexes in nitrogen matrices has been investigated using λ>340 nm radiation of a medium pressure mercury arc. Reaction of the OH radicals from HONO photolysis with CO within the nitrogen lattice site has led to formation of trans and cis-HOCO radicals. The HOCO radicals reacted further with NO via two reaction channels yielding trans and cis-HOC(O)NO or HNO+CO2. Comparison of the observed infrared frequencies and isotope shifts (13C, 18O, and 2H) with the computed frequencies confirmed the assignment of the cis and trans conformers of nitrosoformic acid that have been identified for the first time. In matrices with higher CO concentration the complexes between cis-HOC(O)NO molecule and carbon monoxide were also identified.

The photoinduced isomerization and its implication in the photo-dynamical processes in two simple Schiff bases isolated in solid argon

Two Schiff bases: 2-(1-(methylimino)methyl)-phenol (SMA) and its chlorosubstituted derivative 2-(1-(methylimino)methyl)-6-chlorophenol (SMAC), and SMA complexes with water were studied by infrared matrix isolation spectroscopy and DFT/B3LYP/6-311G++(2d,2p) quantum chemical calculations. SMA and SMAC bases trapped in an argon matrix from the vapor above the liquid and solid samples have the most stable enol conformation with intramolecular O-H···N bonding. Irradiation (λ > 320 nm) leads in both bases to a rotational isomerization reaction in which the scission of the O-H···N bond occurs and the C(H)NCH(3) and OH groups are turned by 180° around the C-C and C-O bonds, respectively. In SMAC a competitive photoreaction channel yields the trans-keto tautomer. The identification of the two SMAC photoproducts evidences that in the excited enol form of this compound two processes compete with each other: the rotational isomerization and intramolecular proton transfer (ESIPT). In the argon matrices doped with SMA and H(2)O the SMA-water complexes were identified and characterized spectroscopically. Interaction of SMA with one or two water molecules does not affect the photochemistry of SMA.

Infrared matrix isolation studies of the N-methylpiperidin-2-one-hydrogen chloride and dimethylformamide-hydrogen chloride complexes

Abstract Infrared spectra are reported of mixtures of N -methylpiperidin-2-one with hydrogen chloride and dimethylformamide with hydrogen chloride in low-temperature matrices. The spectra obtained are characteristic of strongly hydrogen-bonded complexes in which the proton is more or less equally shared between the oxygen and chlorine atoms. The absorption due to the O … H … Cl antisymmetric stretching vibration is extremely broad and diffuse for both complexes.

Infrared matrix isolation spectra of SF6 dimers

Abstract The infrared spectra of 32 SF 6 , 33 SF 6 and 34 SF 6 dimers were studied in argon and nitrogen matrices. The spectra of SF 6 dimers of like and unlike isotopomers were also calculated taking into account the resonance dipole–dipole and dipole-induced dipole interactions between two triply degenerate oscillators. Two absorption bands with site structure are observed for ( 32 SF 6 ) 2 , ( 33 SF 6 ) 2 and ( 34 SF 6 ) 2 in argon; the ν X , Y band is blue shifted and the ν Z band is red shifted from the ν 3 SF 6 band in accordance with calculated spectra. Three and two components of the predicted quadruplets are identified for 32 SF 6 – 34 SF 6 , 32 SF 6 – 33 SF 6 , respectively. In the spectra of (SF 6 ) 2 in nitrogen matrices the splitting of ν X , Y component of the resonance doublet was observed.