Investigation of H atom and free radical behaviour in clathrate hydrates of organic molecules

Abstract

Clathrate hydrates are icy materials composed of a lattice of water molecules containing well-defined cavities which can accommodate small guest molecules. Their large storage capacity makes clathrates attractive media for a variety of gas storage and separation applications, but there is relatively little information on the chemical stability and diffusion of guest molecules. At the fundamental level inter-cage transition energies have been calculated, but the results need to be tested with experimental data. Ideally this should involve single-atom transport, using an isotopic tracer or spin label. Muonium (Mu = µ + e-) qualifies on both counts. As a single-electron atom with the muon as nucleus it may be considered a light isotope of hydrogen. Furthermore muonium and its reaction products may be monitored by muon spin spectroscopy. In recent years we have used this method to probe H-atom and free radical behaviour in clathrate hydrates. The current work extends studies to benzene and acetone clathrate hydrates. Of note is the simultaneous detection of muonium and muoniated radicals in the same sample. This can happen when Mu is trapped in an empty cavity, remote from its reaction partner. Increase in temperature leads to transport of Mu between cages and results in encounters with reactive guest molecules. By studying the temperature dependence of Mu and radical signals, we have been able to determine the activation energy for transport of Mu between cavities.

Free Radical Chemistry of Phosphasilenes

“…This is not simply a result of delayed onset of some frequencies, because the amplitudes of the precession frequencies vary with delay time in a sinusoidal manner. A similar effect has been previously noted for muoniated radicals derived from heteroatomic double bonds: C=O, Si=C, and P=C . A practical consequence of this effect is that “standard” μSR display (no Fourier transform delay) can result in missing a particular signal.…”

Free Radicals Formed by H Atom Addition to Allenes as Determined by Muon Spin Spectroscopy

“…In principle, two-step ionic pathways exist in the end-of-track muon radiolysis spur: either μ + attachment, followed by charge neutralization, or initial electron attachment, followed by muon addition. , One possible indication of such an ionic pathway is delayed formation of the radical product. This is rare, but in recent years, we have reported several instances of related behavior, where the amplitudes of precession frequencies vary sinusoidally with the delay between the muon stop and the time window used to Fourier transform the data. ,− Careful examination of the allene data set revealed some effect for radicals 2b and 2d but not the others. The phenomenon of oscillating signal amplitudes is under examination in other systems where the effect is more marked.…”

“…This is rare, but in recent years we have reported several instances of related behaviour, where the amplitudes of precession frequencies vary sinusoidally with the delay between the muon stop and the time window used to Fourier transform the data. 14,[36][37][38] Careful examination of the allene data set revealed some effect for radicals 2b and 2d but not the others. The phenomenon of oscillating signal amplitudes is under examination in other systems where the effect is more marked.…”

Two-photon chemistry of tetrahydrofuran in clathrate hydrates

“…1b) is granted by the distinct selection rules of 2PA. While this two-photon chemistry (2PC) need not be strictly limited to aqueous matrices, the cavities of clathrate hydrates are highly effective at stabilizing the photochemically produced radicals nearly indefinitely 17–39 making them amenable to observation by spectroscopic methods with inherently low time resolution such as electron spin resonance (ESR).…”