Muons and muonium atoms in solid and liquid methane

Abstract

1270 and 3 1 .O kJ mol-' in the high-and low-temperature phases, respectively. The lower barrier in the high-temperature phase, compared with the amine salt, reflects a looser packing, which is in agreement with a larger entropy change for the acid. Acknowledgment.Muon and muonium spin rotation experiments have been performed in pure liquid and solid methane between 25 and 138 K. Muonium atoms have been observed for the first time in liquid and solid methane. The muonium formation probabilities are found to be 15-20% in both solid and liquid phases. The depolarization rates of muonium atoms increase slightly as a function of temperature and are interpreted as a thermal Mu reaction with methane molecules in liquids and as a spin-lattice interaction in solids. Diamagnetic muon fractions (P,) are found to be strongly temperature dependent; PD increases from 20% at 25 K to 57% at 65 K and stays constant at value 58% above 65 K in both solid and liquid phases. This variation is interpreted as a result of depolarization by muon spin-lattice interactions in methane lattices. An activation energy (52 meV) for spin-lattice relaxation for muons in solid methane was obtained. The diamagnetic fractions of CH,Mu and MuH in condensed phase methane were thus calculated to be 38% and 20%, respectively. IntroductionThe positive muon and muonium (Mu), which is a bound atom of a positive muon and an electron, play a special role in condensed

Hot muonium and muon spur processes in nitrogen and ethane

“…80 It is relevant to comment on results obtained elsewhere in liquid hydrocarbons. Although not directly measured, h D is estimated to be approximately 0.7 in liquid C 2 H 6 (at T ::::: 100 K), based on the yields seen at low pressures 21 for CH 4 and C 2 H 6 and on reported values for liquid methane near 100 K. 81 This estimate appears to be consistent with the high density value reported herein at temperatures near 300 K, both above and below T e , where hD :::::0.5 is seen, with even higher values indica.ted at higher densities (Fig. 8), suggesting that the transi.tion from gas to liquid phase in ethane does not affect the muon polarizations.…”