Shun-ichi Ikawa

Far-infrared optical constants of liquid acetonitrile at 238 to 343 K as measured with a synchrotron radiation source

Far-infrared absorption spectra of liquid acetonitrile at temperatures ranging from 238 to 343 K were measured with a source of synchrotron orbital radiation. On the basis of an optical theory, a theoretical expression for transmittance of a cell filled with liquid was obtained as a function of the optical constants of the liquid. Assuming an analytical form with seven parameters for the absorption coefficients, the refractive indices were analytically calculated by the Kramers-Kronig relation. The parameters of the absorption coefficients were adjusted by least-squares fitting of the theoretical transmittance to the observed transmittance. The resulting optical constants at 298 K were in good agreement with the previously reported results by a laser ATR method. The effect of temperature on the band shape of the absorption is remarkable and will provide an important clue to molecular reorientational dynamics. On the other hand, the molecular dipole moments obtained from the integrated intensities are near...

Far‐infrared absorption of silicon crystals

Far‐infrared absorption coefficients of silicon crystals grown by the Czochralski method (CZ) and by the floating‐zone method (FZ) in the range of 20–200 cm−1 were obtained from transmission measurements at two different thicknesses, allowing for the effect of the multiple internal reflection. The CZ and FZ specimens used were not intentionally doped and had dc resistivities of 9.4±0.3 Ω cm and (5±2)×104 Ω cm, respectively. The impurity‐induced absorption of the CZ crystal is well explained by the Drude model, while the FZ crystal showed only a weak absorption which is attributed to a wing of the intrinsic lattice band of silicon.

Infrared and molecular dynamics study of reorientational relaxation of liquid acetonitrile

The infrared CN stretching bands of acetonitrile in neat liquid and in dilute solution in carbon tetrachloride have been measured at various temperatures. The reorientational and vibrational relaxation times obtained from temperature dependence of the ν2 fundamental bandwidth are consistent with previous Raman results. The reorientational relaxation times are linear in the viscosity divided by the temperature and the proportional constants for the neat liquid and the dilute solution agree with each other within experimental uncertainty. This fact indicates that the effect of the dipole-dipole interaction on the molecular reorientation is included in the viscosity and the proportional constant is characteristic of the molecule, which is consistent with a hydrodynamic theory. Molecular dynamics calculations of liquid acetonitrile were performed at several temperatures with two types of pair potential, with and without Coulomb terms in addition to the atom-atom Lennard-Jones terms. Comparison of the calculated reorientational relaxation times with the experimental results shows that the dipolar interaction plays an important role in the molecular reorientation in liquid acetonitrile.

Near-infrared spectroscopic study of water at high temperatures and pressures

Near-infrared absorption of the OH stretching overtone transition of water has been measured at temperatures and pressures in the ranges of 373–673 K and 20–400 bar, respectively. The absorption profile at 673 K and 400 bar retains a mark of rotational structure, indicating that an appreciable proportion of water molecules can rotate quite freely. The molar absorption intensity decreases linearly with increasing pressure in the low-pressure region. Enthalpy for dimerization has been estimated to be 15±3 kJ/mol from the temperature dependence of the slopes. Plots of the molar absorption intensity against molar concentration are observed to be located on a single curve irrespective of the temperature. This fact indicates that the ratio of hydrogen-bond formation is largely dependent on the molar density only. A good correlation between the molar absorption intensity and the first moments of the band has been found out; this will be useful in the study of aqueous mixtures.

Vibrational spectra and conformation of polyethylene glycol complexed with calcium and magnesium chlorides

Abstract Infrared and Raman spectra of polyethylene glycol (PEG) complexed with calcium and magnesium chlorides have been measured in aqueous solutions and in isolated complexes. Composition of the calcium complex was obtained as 4.4±0.1 (CH 2 CH 2 O unit):1 (CaCl 2 ):4.5±0.5 (H 2 O) by elementary analysis. From these results, the conformation of PEG in the calcium complex has been proposed to be an alternate conbination of two conformational sequences, (-TGT-TG′T-GTT-TTG-) and (-TGT-TG′T-TGT-GTT-TTG-). For the magnesium complex, the conformation of PEG is supposed to be similar to that of crystalline PEG, with repetition of TGT for the -CH 2 CH 2 O units. The difference in the structure between the calcium and magnesium complexes was explained by the difference in the cations size.

Hydrogen bonding of water with aromatic hydrocarbons at high temperature and pressure

Infrared spectra of HDO dissolved in benzene, toluene, ethylbenzene, o-xylene, m-xylene, and mesitylene at 373–473 K and 100 bar have been measured. It is found that the peak positions of the OH bands assigned to monomeric HDO shift to lower wave numbers as ionization energies of the aromatic compounds decrease. It is concluded that the interaction of water and aromatic compounds in the high temperature–pressure mixtures can be described as π-hydrogen bonding as for that in their complexes observed in the low temperature matrices and jet-cooled clusters.

Coupling of intramolecular hydrogen bonding to the cis-to-trans isomerization of a proline imide bond of small model peptides.

A relationship between intramolecular hydrogen bonding and the cis-trans isomerization of a proline imide bond for proline-containing short peptides were studied by proton NMR and infrared spectroscopy using DMSO-d6/CDCl3 mixed solvents. The percentage of the trans form increases with increasing fraction of CDCl3 in the mixed solvents except for compounds without possibility of intramolecular hydrogen bonding. Chemical shift variations of amide protons with solvent mixing ratios were found to be useful for judging whether the amide protons take part in the intramolecular hydrogen bonding to a considerable degree or not. These results and infrared spectra were used to specify intramolecularly hydrogen bonded structures of the peptides. Formation of the 10-membered or 13-membered hydrogen bonded ring which includes the carbonyl group precedent to the prolyl residue facilitates the cis-to-trans isomerization and these hydrogen bonded rings are strong enough to restrict the proline imide bond to the trans form in CDCl3 solution. On the other hand, a 7-membered hydrogen bonded ring is not so effective in restricting the proline imide bond.

Effect of temperature on the infrared band shapes and reorientational and vibrational relaxation of liquid acetonitrile

Abstract Infrared band shapes of the CH stretching ν1 and the CC stretching ν4 vibrations have been measured at various temperatures in the −41–70°C range. The band widths of the fundamental transitions were obtained by resolving the band overlap with hot band transitions and other modes by least-squares fitting with a computer. The reorientational and vibrational relaxation times were obtained by plotting the band widths against the absolute temperature divided by the viscosity. The reorientational relaxation times obtained from the ν1, ν4 and previously studied ν2 band widths are in beautiful agreement with each other and consistent with the previous results by the Raman and NMR methods. To our knowledge, this is the first to obtain the consistent results for the molecular reorientation from different infrared bands without using the Raman results. The vibrational relaxation times for the ν2 and ν4 bands are consistent with the previous Raman results, but, for the ν1 band, the infrared result is at least 20–30% shorter than the Raman results.

Polarized and depolarized Raman spectra of liquid carbon disulfide in the pressure range 0–10 kbar. II. Reorientational and vibrational relaxation

The effect of pressure on the reorientational and the vibrational phase correlation times of liquid carbon disulfide has been determined up to 10 kbar at 295 K from the widths of the isotropic and anisotropic components of the Raman ν1 band. The reorientational correlation time increases with pressure from 1.3 ps at 1 bar to 9 ps at 10 kbar, and the vibrational dephasing time decreases from 19 ps at 1 bar to 5 ps at 10 kbar. The reorientational correlation time is linear in the shear viscosity, and the slope agrees well with the hydrodynamic estimate based on slip at the boundary and the assumption that the carbon disulfide molecule is prolate. The correlation times reported in Ref. 20 at 164–310 K at ambient pressure are the same function of the viscosity divided by the temperature as our values, so showing that the correlation time varies in the same way with the viscosity divided by the temperature whether the viscosity is varied by varying the temperature at constant pressure or by varying the pressur...

Infrared study of water–benzene mixtures at high temperatures and pressures in the two- and one-phase regions

Infrared spectra of water–benzene mixtures have been observed at temperatures and pressures in the 473–648 K and 100–350 bar ranges. The OH stretching band intensities of HDO in the benzene-rich phase in the two-phase region and in the one-phase region were obtained as a function of temperature and pressure. The band intensity, as a measure of water concentration, increases by about three times as the temperature rises from 473 to 523 K, while it is almost independent of pressure in the 100–350 bar range at these temperatures. At higher temperatures, on the contrary, the absorption intensities exhibit remarkable pressure dependence. They increase by an order of magnitude as the pressure increases from 100 to 350 bar. These temperature-pressure dependent changes of water concentration can be properly understood with a phase diagram of the water–benzene mixture. The absolute concentration of water in the benzene-rich phase and in the homogeneous one phase has been estimated from the absorption intensities b...