Search results for "Negative temperature"
showing 4 items of 4 documents
Quantum dynamics of 16O + 36O2 and 18O + 32O2 exchange reactions
2015
We present quantum dynamical investigations of (16)O + (36)O2 and (18)O + (32)O2 exchange reactions using a time-independent quantum mechanical method and an accurate global potential energy surface of ozone [Dawes et al., J. Chem. Phys. 135, 081102 (2011)]. Initial state-selected integral cross sections, rate constants, and Boltzmann averaged thermal rate constants are obtained and compared with earlier experimental and theoretical results. The computed thermal rate constants for the oxygen exchange reactions exhibit a negative temperature dependence, as found experimentally. They are in better agreement with the experiments than the previous studies on the same reactions.
Raman spectra of (PbS)1.18(TiS2)2 misfit compound
2007
Abstract A Raman study on the (PbS)1.18(TiS2)2 semiconductor structure with incommensurate layers (misfit) is reported. The different bands observed in the spectra are attributed to both the TiS2 host layers, at 219 (Eg) and 333 (A1g) cm−1, and the intercalated PbS layers: the LO(Γ), 2LO and 3LO phonons at 203, 412 and 634 cm−1, respectively. A phonon peak probably related to the superposition of TiS2 and PbS vibrations, was observed near 286 cm−1. The decrease of the phonon wave numbers (of the modes located at 203, 333, 412, and 634 cm−1) with increasing laser power pointed out negative temperature coefficients of these modes. A peak appearing with laser power near 151 cm−1 is discussed. …
Ascorbic Acid Oxidation in Sucrose Aqueous Model Systems at Subzero Temperatures
2004
The reduction of Tempol by ascorbic acid in concentrated sucrose solutions was measured by electron paramagnetic resonance (EPR) at temperatures ranging from 16 to −16 °C. This method allowed the determination of the rate constants (k) of this fast reaction, by recording the Tempol reduction as a function of time. The two reactants were initially separated and had to migrate for the reaction to occur. The experimental findings were compared with predicted values according to the equation for diffusion-controlled reaction proposed by Atkins. The experimental reaction rate constants were observed to be lower than the calculated ones. However, the experimental values were found to be controlle…
Translational diffusion coefficients of volatile compounds in various aqueous solutions at low and subzero temperatures.
2005
International audience; Translational diffusion coefficients (D(12)) of volatile compounds were measured in model media with the profile concentration method. The influence of sample temperature (from 25 to -10 degrees C) was studied on translational diffusion in sucrose or maltodextrin solutions at various concentrations. Results show that diffusivity of volatile compounds in sucrose solutions is controlled by temperature, molecule size, and the viscosity of the liquid phase as expected with the Stokes-Einstein equation; moreover, physicochemical interactions between volatile compounds and the medium are determinant for diffusion estimation. At negative temperature, the winding path induce…