Naslov
Hydrodynamic and Nonhydrodynamic Contributions to the Bimolecular Collision Rates of Solute Molecules in Supercooled Bulk Water

Autori
Perić, Ida ; Merunka, Dalibor ; Bales, Barney L. ; Perić, Miroslav

Izvornik
The journal of physical chemistry. B, Condensed matter, materials, surfaces, interfaces & biophysical (1520-6106) 118 (2014), 25; 7128-7135

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Heisenberg spin exchange; dipole-dipole interaction; EPR spectral fitting; Stokes-Einstein equation

Sažetak
Bimolecular collision rate constants of a model solute are measured in water at T = 259–303 K, a range encompassing both normal and supercooled water. A stable, spherical nitroxide spin probe, perdeuterated 2, 2, 6, 6-tetramethyl-4-oxopiperidine-1-oxyl, is studied using electron paramagnetic resonance spectroscopy (EPR), taking advantage of the fact that the rotational correlation time, τR, the mean time between successive spin exchanges within a cage, τRE, and the long-time-averaged spin exchange rate constants, Kex, of the same solute molecule may be measured independently. Thus, long- and short-time translational diffusion behavior may be inferred from Kex and τRE, respectively. In order to measure Kex, the effects of dipole–dipole interactions (DD) on the EPR spectra must be separated, yielding as a bonus the DD broadening rate constants that are related to the dephasing rate constant due to DD, Wdd. We find that both Kex and Wdd behave hydrodynamically ; that is to say they vary monotonically with T/η or η/T, respectively, where η is the shear viscosity, as predicted by the Stokes–Einstein equation. The same is true of the self-diffusion of water. In contrast, τRE does not follow hydrodynamic behavior, varying rather as a linear function of the density reaching a maximum at 276 ± 2 K near where water displays a maximum density.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemija

POVEZANOST RADA