As an attempt to explain some of the many anomalies and unresolved problems, which have been reported about the dynamic behavior of particles and molecules absorbed in crystalline solids, in a recent paper (1) we derived an extension of the Bragg – von Laue scattering law to high-energy colliding particles, which is related also to the Mössbauer effect (2), and was referred to as “reverse Mössbauer effect” (RME). In particular, we proposed an explanation of a specific and well characterized anomalous behavior found in neutron inelastic-scattering spectra (recoiled bands) of methane adsorbed in a zeolite (3). According to RME, a particle in non-equilibrium state with respect to a crystal (colliding with the crystal or adsorbed/absorbed in it, and, set out of thermal equilibrium with the crystal by some external cause), can be scattered by the whole crystal with momentum proportional to a vector representing a reciprocal lattice point. The scattering is expected to occur with a well-defined probability and the momentum transferable to the particle is expected to follow a predictable distribution. As hydrogen is lighter than methane and is adsorbed not only in nanoporous materials, but also is absorbed in a number of metals, we wondered if RME could be present also in H-metal systems and could be detected through some anomalous behavior. RME is essentially a non-equilibrium phenomenon occurring in crystals. Therefore, it could be detected, in principle, by looking for behaviors, which for similar systems differ whether the systems are or not in equilibrium, as well as whether they are crystalline or amorphous. Enhanced diffusion of H under irradiation by ions and electrons (4,5) was observed. Enhanced diffusion was even reported for hydrogen atoms absorbed in bulk Pd in low-temperature scanning tunneling microscopy (6). In a recent paper (7), the interpretation of the anisotropic diffusion of hydrogen in Nickel required unexpectedly high fitting parameters, at least one order of magnitude larger than the values derived from experimental and ab initio studies. The consideration of all these phenomena encouraged us to study the features of the RME for H absorbed in metals, and, as some examples, we evaluated its general features for H absorbed in Ni, Nb, Pd and Ti, because they are among the most frequently studied systems. It was then applied to explain, at least in part, the above reported anomalies. References: 1. P. Demontis, G. B. Suffritti, J. Chem. Phys. 145, 094110 (2016). 2. R. L. Mössbauer, Zeit. Phys. 151, 124 (1958). 3. H. Jobic, Chem. Phys. Lett. 170, 217 (1990). 4. P. Chemov , A.P. Mamontov, Y.I. Tjurin, Y.P. Cherdantsev, J. Nucl. Mater. 233-237, 1118 (1996). 5. I. Chernov, Yu. Tyurin, Yu. P. Cherdantzev, M. Kröning, H. Baumbach, Int. J. Hydrogen Energy 24, 359 (1999) 6. E. C. H. Sykes, L. C. Fernández-Torres, S. U. Nanayakkara, B. A. Mantooth, R. M. Nevin, P. S. Weiss, Proc. Natl. Acad. Sci. U.S.A. 102, 17907 (2005). 7. J. Li, A. Oudriss, A. Metsue, J. Bouhattate, X. Feaugas, Sci. Rep. 7, 45041 (2017).
Reverse Mössbauer Effect as a Source of “Hot” Protons in Hydrogen Absorbing Metals / Suffritti, Giuseppe Baldovino; Demontis, Pierfranco. - Divisione di Chimica Teorica e Computazionale(2017), pp. 17-17. ((Intervento presentato al convegno XXVI Congresso Nazionale della Società Chimica Italiana.