摘要:

Calorimetric measurements of excess enthalpies are reported over the entire composition range for dibutyl ether +n-heptane, +n-deeane, +n-dodecane, and +n-hexadecane at 298.15 K. The results are compared with data from the literature, and a correlation of the excess enthalpies of dibutyl ether +n-alkane mixtures in terms of the Flory theory is described.

ISSN:0008-4042    

DOI:10.1139/v88-090

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Analysis of data from radiation chemical and photochemical studies shows that the reactions of hydroxyl radicals and flavin triplets (Fl3) with amines produce aminyl as well as α-amino radicals. This must be taken into account, since the former tend to oxidise•FlH and FlH−, while the latter are inherently reducing. In the reaction of•OH with piperazine the ratio of aminyl to α-amino radicals at pH 7 is about 60:40. The former undergo complexation to form abonded species, which possess a broad absorption peaking at 520 nm and are inert to lumiflavin (Fl) and paranitroacetophenone on a 30 µs time scale. However, they oxidise dihydrolumifiavin anion (FlH−) to flavin semiquinone radical (•FlH). The α-amino radicals of piperazine reduced lumiflavin to•FlH with a rate constant of 3.3 ± 0.3 × 109 M−1s−1. This rate constant is similar to that observed for the CH3S(ĊH2)2HNH2radical formed from methionine.The 40:60 mixture of α-amino andradicals produced in N2O-saturated piperazine solutions decayed by a second order process with a rate constant of 7.2 × 108 M−1s−1. Similar mixtures of•FlH and thespecies also underwent second order decay (k = 2.7 × 109 M−1s−1) with reoxidation of•FlH to Fl as the major process

ISSN:0008-4042    

DOI:10.1139/v88-091

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The technique of high resolution Brillouin spectroscopy has been used to determine the adiabatic elastic constants of single crystals of β-N2and β-CO as a function of temperature, in an effort to study the α–β phase transition. For all elastic constants, there is an increase of approximately 1%/K on cooling and there is no evidence of further mode softening, even within 0.5 K of the phase transition. Three large single crystals of α-CO were grown. The orientations were determined, by Laue X-ray diffraction, and correlated to the orientations of the parent β-crystals. The β-phase hexagonal basal planes appear to transform to planes of the form {110} in the α-phase cubic structure.

ISSN:0008-4042    

DOI:10.1139/v88-092

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

We have measured the heat capacity of the fast ion conductor PbSnF4at 10.3 < T < 352 K by adiabatic calorimetry. Our results show anomalous values in theCp,min the region 300 < T < 352 K. These are associated with the α–β crystallographic transition reported at 353 K. Because the upper temperature limit of our cryostat is around 354 K, it was impossible to follow the phase transition to completion. A more subtle anomaly in theCp,mwas detected between 130 and 160 K. Standard molar thermodynamic functions are presented at selected temperatures from 5 to 350 K.

ISSN:0008-4042    

DOI:10.1139/v88-093

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The contributions to the free energy of a nematic wetting layer as a function of its thicknesslare analyzed. The longest-range contribution is due to distortion of the nematic director across the film, resulting from different preferred molecular orientations at the two interfaces bounding the film. Van der Waals forces as well as the decaying tails of the interfacial order-parameter profiles yield contributions to the free energy of successively shorter range. These effects lead to crossovers between different scaling régimes for variation of the mean wetting-layer thickness with temperature. Experimental implications of the results are described.

ISSN:0008-4042    

DOI:10.1139/v88-094

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Neutron scattering spectra associated with rotational tunnelling and low frequency vibrations of CH4adsorbed on graphite at 4 K and coverages from 0.2 to 1.5 monolayers are reported. Particular consideration is given to the changes which occur across the commensurate–incommensurate phase transition. It is shown that the incommensurate phase has a domain wall structure and is not a floating phase as had previously been proposed from theory.

ISSN:0008-4042    

DOI:10.1139/v88-095

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The hydrogen bond enthalpies of urea and methyl-substituted ureas with water and DMF have been determined by the pure-base calorimetric method. Transfer enthalpies between water and DMF have been calculated for dilute solutions of the ureas according to a previously developed model. The first solvation sphere of urea in water consists of five water molecules. Solvation spheres are given for other methyl-substituted ureas in water and DMF.

ISSN:0008-4042    

DOI:10.1139/v88-096

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The thermodynamics of the vaporization of liquid zinc chloride has been studied in the temperature range 638–978 K by the modified entrainment method. Enthalpy and entropy changes for vaporization have been derived for the monomer and dimer species. These values are unchanged in a melt contaminated with water at a mole ratio of 1%. The proportion of dimer in the saturated vapour is found to decrease with increasing temperature. The vapour pressure equations for monomer and dimer vaporization, ZnCl2(l) = ZnCl2(g) and 2ZnCl2(l) = Zn2Cl4(g) are In [p10/pӨ] = −(15300 ± 60)K/T + (15.39 ± 0.06) and In [p20/pӨ] = −(11000 ± 970)K/T + (6.5 ± 1.3) for the temperature range 640–980 

ISSN:0008-4042    

DOI:10.1139/v88-097

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A pure methane sample was condensed onto a cold surface (T = 5 K) under conditions used in matrix-isolation spectroscopy. The sample shows a disturbed long range orientational order of CH4II. The free rotor and tunneling transitions are considerably broadened. Stacking faults and defects are believed to cause the disorder. The disorder is largely reduced with increasing annealing temperaturesTabut, surprisingly, even atthe long range order is not fully reestablished.

ISSN:0008-4042    

DOI:10.1139/v88-098

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The absorption spectra of adamantanethione (I), thiofenchone (II), and thiocamphor (III) have been measured in the quartz ultraviolet region in both the vapor phase and in perfluoroalkane solutions. Rydberg as well as π → π* transitions are identified in the gas phase spectra, and are discussed in terms of the known photochemistry of these compounds.

ISSN:0008-4042    

DOI:10.1139/v88-099

出版商:NRC Research Press    

年代:1988

数据来源: NRC