Ortho-para conversion between the nuclear spin isomers of the quantum rotor H2O: water molecules entrapped inside C60 (H2O@C60)
Spin-symmetry conversion between the nuclear spin isomers of quantum rotors is an interesting phenomenon to fundamental physics. In our studies to date we have found that conversion between ortho-hydrogen and para-hydrogen trapped inside fullerene cages is undetectable over the timescale of experiments; many days. However, recent NMR data on water@C60 emerging from the laboratory of Malcolm Levitt (CI on this proposal) suggests that conversion between ortho-H2O and para-H2O occurs on a timescale of hours at low temperature. Furthermore, the data shows there are two distinct components within the sample, one for which there is ortho-para conversion (timescale hours) and a second for which there is no conversion over long timescales. In this experiment, the conversion time will be measured by monitoring the populations of ortho- and para-water. This will be achieved by making a temperature step and studying the time evolution of the amplitudes of the 101 - 000 rotational line of the water molecule in neutron energy loss and gain. The conversion time will be measured as a function of temperature.
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HORSEWILL Anthony J.; GOH Kelvin; JOHNSON Mark Robert; LEVITT Malcolm; ROLS Stephane and TURRO Nicholas. (2013). Ortho-para conversion between the nuclear spin isomers of the quantum rotor H2O: water molecules entrapped inside C60 (H2O@C60). Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.7-05-416
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