Kazuyasu Ibuki

Effect of pressure on the transport properties of ionic liquids: 1-alkyl-3-methylimidazolium salts.

The self-diffusion coefficients (D) of the cation and anion in the ionic liquids 1-hexyl-3-methylimidazolium and 1-octyl-3-methylimidazolium hexafluorophosphates ([HMIM]PF6 and [OMIM]PF6) and 1-butyl-3-methylimidazolium and 1-octyl-3-methylimidazolium tetrafluoroborates ([BMIM]BF4) and ([OMIM]BF4) have been determined together with the electrical conductivities (kappa) of [HMIM]PF6 and [BMIM]BF4 under high pressure. The pressure effect on the transport coefficients is discussed in terms of velocity cross-correlation coefficients (VCCs or fij), the Nernst-Einstein equation (ionic diffusivity-conductivity), and the fractional form of the Stokes-Einstein relation (viscosity-conductivity and viscosity-diffusivity). The (mass-fixed frame of reference) VCCs for the cation-cation, anion-anion, and cation-anion pairs are all negative and strongly pressure dependent, increasing (becoming less negative) with increasing pressure. VCCs are the more positive for the stronger ion-velocity correlations; therefore, f+ - is least negative in each case. In general, f- - is less negative than f+ +, indicating a smaller correlation of velocities of distinct cations than that for distinct anions. However, for [OMIM]PF6, the like-ion fii are very similar to one another. Plots of the VCCs for a given ion-ion correlation against fluidity (reciprocal viscosity) show the fij to be strongly correlated with the viscosity as either temperature or pressure are varied, that is, fij approximately fij(eta). The Nernst-Einstein deviation parameter, Delta, is nearly constant for each salt under the conditions examined. It is emphasized that nonzero values of Delta are not necessarily due to ion pairing but result from differences between the like-ion and unlike-ion VCCs, because Delta is proportional to (f+ + + f- - - 2 f+ -). The diffusion and molar conductivity (Lambda) data are found to fit fractional forms of the Stokes-Einstein relationship, (LambdaT) proportional, variant (T/eta)(t) and Di proportional, variant (T/eta)(t), with t=(0.90+/-0.05) for all these ionic liquids, independent of both temperature and pressure within the ranges studied.

Construction of a subpicosecond double-beam laser photolysis system utilizing a femtosecond Ti:sapphire oscillator and three Ti:sapphire amplifiers (a regenerative amplifier and two double passed linear amplifiers), and measurements of the transient absorption spectra by a pump-probe method

A double-beam Ti:sapphire laser photolysis system has been constructed for measurements of the subpicosecond transient absorption spectra by a pump-probe method. Although the spectroscopic characteristics tested for the practical availability are satisfactory enough, the transient absorption spectrum thus obtained exhibits an artificial time-dependent spectral change owing to the group velocity dispersion of the probing light pulse. Hence, its wavelength-dependent arrival time to the sample cell is determined utilizing the optical Kerr effect induced in carbon tetrachloride and the true transient absorption spectrum (the corrected spectrum) at a given delay-line setting is calculated by a microcomputer using a great number of uncorrected transient absorption spectra obtained at different delay-line settings. Interestingly, the corrected singlet-singlet absorption band (band C with a lifetime of 0.8 ps) obtained for the lowest excited singlet state of 9-nitroanthracene in cyclohexane really shifts with tim...

Pressure and temperature effects on 2H spin-lattice relaxation times and 1H chemical shifts in tert-butyl alcohol- and urea-D2O solutions

The pressure and temperature effects of hydrophobic hydration were studied by NMR spectroscopy. The 1H chemical shifts (δ) were measured at 7.7, 29.9, and 48.4 °C under high pressure up to 294 MPa for HDO contained as impurity in neat D2O, 1 mol kg−1 tert-butyl alcohol (TBA)-D2O, and 1 mol kg−1 urea-D2O solutions, for the methyl group of TBA in the TBA-D2O solution, and for the amino group of urea in the urea-D2O solution. The 2H spin-lattice relaxation times (T1) were measured under the same conditions as the chemical shift measurements for D2O in neat D2O, TBA-D2O and urea-D2O solutions with organic contents up to 8 mol%. The following features are observed for the pressure effect on δ (HDO) and 2H-T1 in TBA-D2O solutions: (1) The δ (HDO) exhibits a downfield shift relative to that in neat D2O, and the difference of δ (HDO) between TBA solution and neat D2O becomes larger with increasing pressure at lower temperature. (2) The decrement of the rotational correlation time of water in the hydration shell o...

Estimated ionicB-coefficients from NMR measurements in aqueous electrolyte solutions

Abstract17O-NMR spin-lattice relaxation timesT1 of D2O molecules were measured at 5–85°C in D2O solutions of alkali metal halides (LiCl∼CsCl, KBr, and KI), DCl, KOD, Ph4PCl, NaPh4B, and tetraalkylammonium bromides (Me4NBr∼Am4NBr) in the concentration range 0.1–1.4 mol-kg−1 TheB-coefficients of the electrolytes obtained from the concentration dependence of relaxation ratesR1=1/T1 were divided into the ionicB-coefficients by three methods: (i) the assumption ofB (K+)=B(Cl−), (ii) the assumption ofB(Ph4P+)=B(Ph4B−), and (iii) the use ofB(Br−) obtained from a series ofB(R4NBr). It was found that Methods (ii) and (iii) resulted in an abnormal temperature dependence of theB-coefficients of alkali metal ions and a negative values of rotational correlation times τc at lower temperatures for hydroxide and halide ions. These results suggest that the methods based on the van der Waals volume are not adequate for the ionic separation of NMRB-coefficients. From the analysis using the assumption ofB(K+)=B(Cl−), it was found that D3O+, OD−, and Me4N+ ions are the intermediates between structure makers and breakers, and that the hydrophobicity of phenyl groups is weaker than that of alkyl groups due to the interactions between water molecules and π-electrons in phenyl groups.

Electric conductivities of 1:1 electrolytes in liquid methanol along the liquid–vapor coexistence curve up to the critical temperature. I. NaCl, KCl, and CsCl solutions

The molar conductivities Lambda of NaCl, KCl, and CsCl in liquid methanol were measured in the concentration range of (0.3-2.0) x 10(-3) mol dm(-3) and the temperature range of 60-240 degrees C along the liquid-vapor coexistence curve. The temperature range corresponds to the solvent density range of (2.78-1.55)rhoc, where rhoc = 0.2756 g cm(-3) is the critical density of methanol. The concentration dependence of Lambda at each temperature and density (pressure) has been analyzed by the Fuoss-Chen-Justice equation to obtain the limiting molar conductivity Lambda0 and the molar association constant KA. For all the electrolytes studied, Lambda0 increased almost linearly with decreasing density at densities above 2.0rhoc, while the opposite tendency was observed at lower densities. The relative contribution of the nonhydrodynamic effect on the translational friction coefficient zeta was estimated in terms of Deltazeta/zeta, where the residual friction coefficient Deltazeta is the difference between zeta and the Stokes friction coefficient zetaS. At densities above 2.0rhoc, Deltazeta/zeta increased with decreasing density though zeta and Deltazeta decrease, and the tendencies are common for all the ions studied. The density dependences of zeta and Deltazeta/zeta were explained well by the Hubbard-Onsager (HO) dielectric friction theory based on the sphere-in-continuum model. At densities below 2.0rhoc, however, the experimental results cannot be explained by the HO theory.

Effect of potential of mean force on short-time dynamics of a diffusion-controlled reaction in a hard-sphere fluid

We calculated the time-dependent rate constant of a diffusion-controlled reaction between hard-spheres in a hard-sphere fluid at short times starting from the Fokker–Planck–Kramers equation combined with the approximation of half-range Maxwellian velocity distributions. For the potential function, we employed the potential of mean force (PMF) obtained from the equilibrium radial distribution function. The rate constant at short times was much larger than that neglecting the PMF effect, though the steady state rate constant did not sensitively depend on the PMF effect. This indicates that the effect of the initial distribution of the reactants is important in determining the rate constant at short times. The results were compared with a computer simulation. The dependences of the survival probability of a target on the time, the transmission coefficient, and the reactant concentration were examined, and satisfactory agreements between the calculation and the simulation were obtained at a relatively low den...

Improved treatment of inertia and non-Markovian effects on short-time dynamics of diffusion-controlled reaction based on generalized diffusion equation

Starting from a generalized diffusion equation and the Collins–Kimball boundary condition, we investigated the inertia and the non-Markovian effects on the time-dependent rate constant of a diffusion-controlled reaction at short times. In the short-time limit, we obtained the rate constant analytically, and found that the rate constant was independent of the friction coefficient, and was always smaller than the result of the classical Smoluchowski–Collins–Kimball (SCK) theory in which both of the inertia and the non-Markovian effects were neglected. At finite times, we obtained the rate constant numerically, and found that the decay of the rate constant was slower than that of the SCK result. When the non-Markovian effect became larger, the decay became much slower. Our results were consistent with a relevant theory based on a generalized Fokker–Planck equation. The results were compared with computer simulations, and a good agreement was obtained for the case of the maximum reactivity.

Pressure and solvent isotope effects on the mobility of monovalent cations in water

Limiting molar conductivities of alkali metal chlorides (LiCl to CsCl) and tetraalkylammonium bromides (Me4NBr to Bu4NBr) in H2O and D2O were determined at 25 °C as a function of pressure up to 196.1 MPa. The limiting molar conductivities of the ions were obtained with the aid of transference numbers of KCl under high pressure, and transformed into the residual friction coefficients Δζobs to see what kinds of factors are important in the mechanism of ion migration. The pressure and solvent isotope effects on Δζobs of the Li+ ion agree qualitatively with the predictions of the Hubbard–Onsager (HO) dielectric friction theory, which indicates that dielectric friction plays an important role for smaller ions. However, the Cs+ ion shows opposite pressure and solvent isotope effects. For the R4N+ ions, Δζobs increases with an increase in the ionic radius and the pressure, opposite to the predictions of the HO theory. The increase in Δζobs for large R4N+ ions with increasing pressure suggests that the structure ...

A rapid decay channel of the lowest excited singlet state of 9-benzoyl-10-nitroanthracene generating 9-benzoyl-10-anthryloxy radical and nitrogen (II) oxide

Abstract In cyclohexane at room temperature, the lowest excited singlet state ( 1 BNA ∗ with a lifetime of 0.8 ps) of 9-benzoyl-10-nitroanthracene has a broad absorption band and its shift to shorter wavelengths with time can be ascribed to the wide wavelength-range superposition of an absorption band which increases and then decreases with time constants of 0.8 and 1.8 ps, respectively. Hence, this band is assigned to the absorption of a higher excited triplet state of 9-benzoyl-10-nitroanthracene or that of an intermediate (INT) shown later (or 9-benzoyl-10-nitrite) which is formed from 1 BNA ∗ and decomposes into 9-benzoyl-10-anthryloxy radical and nitrogen (II) oxide finally.

Fokker–Planck–Kramers equation treatment of dynamics of diffusion-controlled reactions using continuous velocity distribution in three dimensions

A theory has been developed for the short-time dynamics of diffusion-controlled reactions based on the Fokker–Planck–Kramers equation (FPKE) in three dimensions. A continuous velocity distribution function has been proposed to solve the FPKE approximately. The present theory agrees better with the Langevin dynamics results than the earlier theory using a discontinuous velocity distribution. This indicates the validity of the present theory in three dimensions, because the Langevin dynamics results can be assumed to be the exact solutions to the FPKE. The theory is compared with molecular dynamics (MD) simulations in Lennard-Jones fluids to examine the applicability for realistic systems. The present theory predicts a somewhat smaller rate constant than the MD simulation in the time range of a few picoseconds. The discrepancies can be explained qualitatively in terms of the non-Markovian effect on the molecular motions.