The contribution of tunnelling to the diffusion of protons and deuterons in rare gas solids

The stability and diffusion of protons and deuterons in rare gas matrices are reexamined. These are known to be stabilized in rare gas matrices in the form of linear, centrosymmetric Rg₂H⁺ cations. The elementary step in their diffusion, displacement from one Rg–Rg bond to a neighboring one, can be modelled as an isomerization of the triangular Rg₃H⁺ cation. Using an analytic approximation for thermally averaged transmission coefficients for tunnelling through and reflection by a truncated parabolic potential barrier (R.T. Skodje and D.G. Truhlar,J. Phys. Chem. 85, 624 (1981)) we calculate the rate constants for this elementary diffusion step. The calculated rate constants are consistent with all experimental observations, and confirm that tunnelling makes the dominant contribution to the diffusion of protons and deuterons in rare gas solids. Deuteration reduces the tunnelling rates by 5 to 8 orders of magnitude, which agrees with the observation that D⁺ in rare gas solids is signficantly more stable than H⁺

Oxygen-driven relaxation processes in pre-irradiated Ar cryocrystals

Relaxation processes in oxygen-containing Ar cryocrystals pre-irradiated by low-energy electrons are studied with the focus on the role of diffusion controlled atom-atom recombination reaction of oxygen in the relaxation cascades. The results of correlated in real time measurements of thermally stimulated phenomena are presented. The experiments have been performed using activation spectroscopy methods — thermally stimulated exoelectron emission and spectrally resolved thermally stimulated luminescence. Solid evidence of the radiative mechanism of electron detrapping triggering the relaxation cascades is obtained

Thermally stimulated exoelectron emission from solid Xe

Thermally-stimulated emission of exoelectrons and photons from solid Xe pre-irradiated by low-energy electrons were studied. A high sensitivity of thermally-stimulated luminescence (TSL) and thermally-stimulated exoelectron emission (TSEE) to sample prehistory was demonstrated. It was shown that electron traps in unannealed samples are characterized by a much broader distribution of trap levels in comparison with annealed samples and their concentration exceeds in number that in annealed samples. Both phenomena, TSL and TSEE, were found to be triggered by release of electrons from the same kind of traps. The data obtained suggest a competition between two relaxation channels: charge recombination and electron transport terminated by TSL and TSEE. It was found that TSEE predominates at low temperatures while at higher temperatures TSL prevails. An additional relaxation channel, a photon-stimulated exoelectron emission from pre-irradiated solid Xe, was revealed

Stimulated by laser light exoelectron emission from solid Ar pre-irradiated by an electron beam

Spatially separated stable charge centers, self-trapped holes and trapped electrons, were generated in Ar cryocrystals by a low-energy electron beam. A combination of the cathodoluminescence (CL) and photon- stimulated exoelectron emission (PSEE) methods was used to monitor center formation and selected relaxation channel – exoelectron emission. It was found that photon-promoted electron current decreased exponentially under irradiation with the laser operating in the visible range. Influence of the laser parameters (power and wavelength) on the characteristic lifetime of exoelectron emission is discussed. Effective bleaching of the low-temperature peaks of thermally stimulated exoelectron emission by the laser light in a visible range was observed

Anomalous low-temperature “post-desorption” from solid nitrogen

Anomalous low-temperature post-desorption (ALTpD) from the surface of nominally pure solid nitrogen pre-liminary irradiated by an electron beam was detected for the first time. The study was performed using a combi-nation of activation spectroscopy methods — thermally stimulated exoelectron emission (TSEE) and spectrally resolved thermally stimulated luminescence (TSL) — with detection of the ALTpD yield. Charge recombination reactions are considered to be the stimulating factor for the desorption from pre-irradiated α-phase solid nitrogen

Thermoactivation spectroscopy of solid Ar doped with N₂

A new modification of low-temperature activation spectroscopy technique for real-time correlated study of relaxation processes in cryogenic solids was developed. This enabled us to measure simultaneously thermally stimulated exoelectron emission (TSEE) and spectrally resolved thermally stimulated luminescence (TSL) in the range from 200 to 1100 nm. This paper presents the results on TSL and TSEE from solid Ar doped with N₂ exposed to irradiation by low-energy electron beam (500 eV) during deposition. The TSEE and TSL yields were measured at the heating rate of 3.2 K/min. The emissions of molecular (A³Σu⁺ → X¹Σg⁺ transition) and atomic (²D → ⁴S transition) nitrogen in the TSL spectra and their temperature behavior were studied. Drastic changes in the intensity distribution of the molecular progression were observed with temperature rise. In low-temperature range «hot» vibrationally unrelaxed transitions were detected in contrast to «cold» vibrationally relaxed transitions observed in «high» temperature TSL. The mechanisms of the processes resulting in TSL in whole temperature range of Ar solid occurrence are suggested

Relaxation channels and transfer of energy stored by pre-irradiated rare gas solids

The processes of energy relaxation in rare gas solids pre-irradiated with an electron beam are discussed. We studied the emission of exoelectrons and photons from RGS. Investigations were performed by a set of activation spectroscopy methods applied simultaneously to each sample. Photon-stimulated exoelectron emission from solid Ne was observed for the first time

Formation of (Xe2H)* centers in solid Xe via recombination: nonstationary luminescence and «internal electron emission»

The formation of excimers (Xe2H)* in solid Xe doped with molecular hydrogen under electron beam is studied using the original two-stage technique of nonstationary (NS) cathodoluminescence (CL) in combination with the current activation spectroscopy method — thermally stimulated exoelectron emission (TSEE). Charged species were generated using a high-density electron beam. The species produced were then probed with a lowdensity beam on gradual sample heating. The near UV emission of the (Xe2H)* was used to monitor the neutralization process. It is found that the temperature behavior of the NS CL band of (Xe2H)* clearly correlates with the yield of TSEE measured after identical pre-irradiation of the sample. The fingerprints of the thermally stimulated detrapping of electrons — «internal electron emission» in the spectrum of NS CL point to the essential role of neutralization reaction in the stability of the proton solvated by rare-gas atoms