Note: Anharmonicity of quasi-lattice modes in glass and super-fragile liquid states of decahydroisoqinoline: C ₉H ₁₇N

One of the most fragile of all molecular liquids, perhydronapthalene (decalin), was recently shown to have quite abnormal low frequency (quasi-lattice) vibrational modes, implying extreme anharmonicity. A molecular liquid of similar structure and fragility, but chemically suited to structural modification, has been found to lose its fragility on accepting a proton from simple mineral acids (forming a protic ionic liquid). Here we show, again by low energy neutron scattering studies, that this derivatizable liquid, decahydroisoquinoline, has the same highly anharmonic quasi-lattice characteristics as decalin (thus inviting a future comparison with the quasi-lattice character of the non-fragile derivatives).