Title: Indirect observation of molecular disassociation in solid benzene at low temperatures,
Abstract: The molecular dynamics of solid benzene are extremely complex; especially
below 77 K, its inner mechanics remain mostly unexplored. Benzene is also a
prototypical molecular crystal that becomes energetically frustrated at low
temperatures and usually unusual phenomena accompanies such scenarios. We
performed dielectric constant measurements on solid benzene down to 5 K and
observed a previously unidentified minimum in the imaginary part of the
dielectric constant at Tm=17.9 K. Results obtained on deuterated solid benzene
(C6D6, where D is deuterium) show an isotope effect in the form of a shift of
the critical temperature to Tm'=18.9 K. Our findings indicate that at Tm, only
the protons without the carbon atoms continue again to undergo rotational
tunneling about the hexad axes. The deuterons appear to do the same accounting
for an indirect observation of a continued and sustained 12-body tunneling
event. We discuss how similar experiments performed on hydrogen-based molecular
crystals can be exploited to help us obtain more insight on the quantum
mechanics of many-body tunneling.