1 research outputs found
EPR Evidence of Liquid Water in Ice: An Intrinsic Property of Water or a Self-Confinement Effect?
Liquid
water (LW) existence in pure ice below 273 K has been a
controversial aspect primarily because of the lack of experimental
evidence. Recently, electron paramagnetic resonance (EPR) has been
used to study deeply supercooled water in a rapidly frozen polycrystalline
ice. The same technique can also be used to probe the presence of
LW in polycrystalline ice that has formed through a more conventional,
slow cooling one. In this context, the present study aims to emphasize
that in case of an external probe involving techniques such as EPR,
the results are influenced by the binary phase (BP) diagram of the
probe-water system, which also predicts the existence of LW domains
in ice, up to the eutectic point. Here we report the results of our
such EPR spin-probe studies on water, which demonstrate that smaller
the concentration of the probe stronger is the EPR evidence of liquid
domains in polycrystalline ice. We used computer simulations based
on stochastic Liouville theory to analyze the lineshapes of the EPR
spectra. We show that the presence of the spin probe modifies the
BP diagram of water, at very low concentrations of the spin probe.
The spin probe thus acts, not like a passive reporter of the behavior
of the solvent and its environment, but as an active impurity to influence
the solvent. We show that there exists a lower critical concentration,
below which BP diagram needs to be modified, by incorporating the
effect of confinement of the spin probe. With this approach, we demonstrate
that the observed EPR evidence of LW domains in ice can be accounted
for by the modified BP diagram of the probe–water system. The
present work highlights the importance of taking cognizance of the
possibility of spin probes affecting the host systems, when interpreting
the EPR (or any other probe based spectroscopic) results of phase
transitions of host, as its ignorance may lead to serious misinterpretations