Claus J. Nielsen

KINETIC STUDY OF GAS-PHASE REACTIONS OF PINONALDEHYDE AND STRUCTURALLY RELATED COMPOUNDS

Rate constants for the reactions of OH, NO3, and O3 with pinonaldehyde and the structurally related compounds 3-methylbutanal, 3-methylbutan-2-one, cyclobutylmethylketone, and 2,2,3-trimethyl-cyclobutyl-1-ethanone have been measured at using on-line Fourier transform infrared spectroscopy. The rate constants obtained for the reactions with pinonaldehyde were: ,

Molecular complexes of nitric acid with various bases studied by matrix isolation infrared spectroscopy

Abstract The interaction of nitric acid with a number of bases has been investigated by infrared spectroscopy in low-temperature matrices (principally argon). The spectra show that nitrogen interacts strongly and specifically with nitric acid in argon matrices. Carbon monoxide behaves in a similar manner to nitrogen, forming complexes with the structure OC⋯HONO 2 . With water and dimethyl ether, hydrogen-bonded complexes of the type R 2 O ⋯ HONO 2 were formed, and with ammonia a similar complex H 3 N ⋯ HONO 2 was apparent. The strength of interaction, as evidenced by the shifts in the OH vibrational modes of the nitric acid, increased from nitrogen, through carbon monoxide, water and dimethyl ether, to ammonia.

Infrared matrix isolation study of H2SO4 and its complexes with H2O

Infrared spectra of H2SO4 vapors, which also include H2O and SO3, were trapped in argon matrices. Vibrational assignments for monomeric H2SO4 were established and additional bands were assigned to the (H2SO4)2, (H2O)·(H2SO4) and (H2O)2·(H2SO4) species. For the (H2O)·(H2SO4) complex, several isomers are shown to exist, the most stable being H2O·HOSO2OH. Temperature reversible changes in several bands of the latter complex are discussed in analogy to the trimeric (H2O)3 complex. The H2O and H2SO4 molecules dispersed in the argon solid do not affect the stabilization of a mixed (H2O)m·(SO3)n complex. No spectral evidence for ionized species due to proton transfer was found in the matrix samples investigated.

MOLECULAR COMPLEXES OF NITRIC ACID WITH N2, CO AND NO STUDIED BY MATRIX ISOLATION IR SPECTROSCOPY

The interaction of nitric acid with dinitrogen, carbon monoxide and nitric oxide has been investigated by IR spectroscopy in low-temperature argon matrices. The spectra show that under these conditions N2 interacts strongly and specifically with HNO3, forming several distinct 1:1 complexes. The probable structures of these complexes are discussed. CO behaves in a similar manner to N2, forming complexes of the type OC⋯H—ONO2; weak bands due to a CO⋯H—ONO2 complex were generated by photolysis. For NO, complexes of HNO3 were observed with both monomeric and dimeric NO. The strength of interaction with HNO3 was found to increase in the order N2 < NO < CO.

Fourier transform infrared spectrometry studies of surface and bulk porosity of water ice

Abstract Water ices used as mimics in laboratory studies of heterogeneous chemical reactions have been investigated by FTIR. Water ice as vacuum deposited onto a CsI substrate at 5 K was found to be essentially non-porous. Inert gas pre-deposition and co-deposition followed by temperature cycling induced surface and bulk porosity into the produced layers. Porosity was monitored by the shape and position of the 3300 cm−1 coupled water band, by the dangling OH high frequency mode, and by the modes of hydrogen bonded and trapped CO. The highest amount of dangling OH bonds was revealed with Ar/H2O deposition mixtures whereas the highest degree of bulk porosity was achieved with neon as co-deposited gas.

Spectroscopic studies of ethylene-propylene copolymers in the near- and mid-infrared regions

Abstract Methods were derived to determine the monomer composition in block (heterophasic) ethylene-propylene copolymer samples by means of infrared spectroscopy in the mid- (MIR) and near-infrared (NIR) regions. Reference samples of known composition, ranging from 3.3 to 70.4 mol% of ethylene, having approximately the same crystallinity, were employed to standardize the method by which three commercial grades of copolymers were analysed. In the 6200-4500 and 4500-3600 cm−1 ranges, 20 and 23 absorption bands, respectively, were observed, but none of these were pure polyethylene bands. In spite of extended band separation and the use of band areas, the best accuracy in this region was obtained using peak heights. Approximately ten polypropylene bands and two polyethylene bands were separated in the MIR region (1200-600 cm−1), and band areas were successfully employed. The CO2 vapour band at 668 cm−1 interfered with the polyethylene doublet at 720 and 730 cm−1. Additional studies were carried out at low temperatures in the range 300-90 K to study the effect of temperature on the calibration graphs. When the PE bands at 730 and 720 cm−1 were ratioed against the PP band at 900 cm−1 as a function of temperature, a sharp break in the curve was observed at the position of the glass transition temperatures.

Infrared absorption cross section, radiative forcing, and GWP of four hydrofluoro(poly)ethers

Quantitative infrared cross-sections of the unbranched hydro#uoro(poly)ethers CHF 2 OCHF 2 , CHF 2 OCF 2 OCHF 2 and CHF 2 OCF 2 CF 2 OCHF 2 have been obtained at 298 K in the region 25}4000 cm~1. Radiative forcing calculations have been performed for these compounds and for CHF 2 OCF 2 OCF 2 CF 2 OCHF 2 , and the values found per molecule are high compared to those of other CFCs and CFC replacements. Atmospheric lifetimes, calculated on the basis of experimental reaction rates with OH radicals, and global warming potentials are presented for all four compounds. ( 1999 Elsevier Science Ltd. All rights reserved.

Experimental and theoretical study of the F, Cl and Br reactions with formaldehyde and acetaldehyde

The vapour phase reactions of formaldehyde, formaldehyde-d2, 13C-formaldehyde, acetaldehyde, acetaldehyde-1-d1, acetaldehyde-2,2,2-d3, and acetaldehyde-d4 with Cl and Br atoms were studied at 298±2 K and 1013±10 hPa using long-path FTIR detection. For formaldehyde the only products observed were HCl, HBr and CO; for acetaldehyde the product distribution suggests one dominant channel: CH3CHO+X→CH3CO+HX. The kinetic isotope effects at 298 K were determined by the relative rate method as: kCl+HCHO/kCl+DCDO=1.302±0.014, kCl+H13CHO/kCl+DCDO=1.217±0.025, kBr+HCHO/kBr+DCDO=7.5±0.4 and kBr+H13CHO/kBr+DCDO=6.8±0.4, kCl+CH3CHO/kCl+CH3CDO=1.343±0.023, kCl+CH3CHO/kCl+CD3CDO=1.323±0.018, kCl+CD3CHO/kCl+CH3CDO=1.345±0.015, kCl+CD3CHO/kCl+CD3CDO=1.394±0.021, kBr+CH3CHO/kBr+CH3CDO=3.98±0.26, kBr+CH3CHO/kBr+CD3CDO=3.79±0.29, kBr+CD3CHO/kBr+CH3CDO=4.02±0.10 and kBr+CD3CHO/kBr+CD3CDO=3.96±0.20. Quoted errors represent 3σ from the statistical analyses and do not include possible systematic errors. The reactions of F, Cl and Br atoms with formaldehyde and acetaldehyde were studied by quantum chemical methods on the MP2 level of theory using the cc-pVDZ basis sets. The calculations indicate the existence of a weak adduct in which the halogen atoms are bonded to the aldehydic oxygen. Transition states of the reactions X+HCHO→HX+CHO and X+CH3CHO→HX+CH3CO (X=F, Cl, Br) were located. Reaction rate coefficients and kinetic isotope effects, calculated from conventional transition state theory are compared to experimental data and the deviations are tentatively attributed to adduct formation.

IR spectrum of molecular complexes of sulfuric acid with N2 and NO trapped in solid argon

The IR spectra of vapours above neat sulfuric acid trapped, mixed with varying amounts of N2 and NO gases in argon matrices are reported. Absorptions due to 1:1 (N2)·(H2O), (N2)·(H2SO4), (NO)·(H2O), (NO)·(H2SO4) and (N2O2)·(H2SO4) dimeric complexes were identified in all relevant spectral regions. The interactions of nitrogen and nitrogen oxides with SO3 do not indicate complex formation. A T-shaped attachment of N2 to H2SO4, and an O-end interaction of the nitrogen oxide monomer and dimer with the OH groups of H2SO4 is suggested. The formation of the complex species is by surface diffusion during deposition and not a result of vapour phase equilibria.

The vibrational spectra including matrix isolation and conformations of 1-chloro-1-fluorocyclobutane and 1-chloro-1,2,2-trifluorocyclobutane

Abstract The IR and Raman spectra of 1-chloro-1-fluorocyclobutane (CFCB) and 1-chloro-1,2,2-trifluorocyclobutane (CFCB) were recorded in various phases and at different temperatures, and included IR matrix spectra in argon and nitrogen matrices using the hot nozzle method. Both compounds have two conformers in the vapour and liquid states. CTFCB crystallized as one distinct conformer, while two conformers were present in all solid state spectra of CTFCB. The argon matrix spectrum of CFCB contained only one conformer at 13 K, suggesting a barrier lower than 5 kJ mol−1 between the conformers. In both the argon and nitrogen matrix spectra of CTFCB two conformers were observed, although the concentrations of the less stable conformer were lower than in the vapour. This suggests a partial conversion to the stable conformer during deposition and a barrier slightly higher than 6 kJ mol−1. The enthalpy difference ΔH° between the conformers was 2.2 kJ mol−1 for CFCB in the liquid and 2.7 and 2.9 kJ mol−1 in the vapour and liquid, respectively, for CTFCB. Ab initio calculations were carried out for both compounds using the 3-21G* and 6-31G* basis sets. For CFCB, both calculations gave the conformer with the fluorine atom equatorial as the more stable. For CTFCB, the smaller basis set also gave the conformer with equatorial fluorine as the more stable while the opposite was predicted with the larger basis set. Fairly complete assignments for both conformers of both compounds were made with the aid of normal coordinate calculations employing scaled ab initio force constants. Agreement was excellent between calculation and experiment for the case in which the more stable conformer was that with fluorine equatorial but impossible to achieve with fluorine axial.