A NMR study of solid methane: The low temperature phase transition

Abstract

Proton magnetic resonance measurements have been carried out between 5 and 80 K and up to pressures of 3 kbar in order to investigate two phase transitions in solid methane. The P versus T plot of the low temperature (β-γ) phase transition is strongly curved and, consequently, this transition can only be found at pressures above 200 atm. The effects of the tunnel splittings between the ground states of the three spin isomers on the curvature of this transition line are discussed.