Advances in Spectroscopy of Subthreshold Inelastic Radiation-Induced Processes in Cryocrystals

Abstract

A review is given on the recent spectroscopic studies of the electronic excitation induced processes of large-scale atomic displacements in atomic cryocrystals, including defect formation, atomic and molecular desorption.

Excitonic mechanisms of inelastic radiation-induced processes in rare-gas solids

“…The electronic properties of RGS have been under investigation since seventies and now the overall picture of creation and trapping of electronic excitations is basically complete. Because of strong interaction with phonons the excitons and holes in RGS are self-trapped, and a wide range of electronic excitations are created in samples: free excitons, atomic-like (A-STE) and molecular-like self-trapped excitons (M-STE), molecular-like self-trapped holes and electrons trapped at lattice imperfections [2][3][4][5][6]. The coexistence of free and trapped excitations and, as a result, the presence of a wide range of luminescence bands with well studied internal structure in the emission spectra of RGS enable one to reveal the energy relaxation channels and to detect the elementary steps in lattice rearrangement.…”

“…In the row Xe, Kr, Ar, Ne the atomic plarizability decreases as well as the crystal electron affinity; the latter becomes negative in the case of solid Ar and Ne [2][3][4][5][6]. As a consequence, the main channel of exciton selftrapping in Xe and Kr is the formation of M-STE, which is equivalent to a molecular dimer R 2 * imbedded into the host lattice (R=rare gas atom).…”

“…The high quantum yield of molecular luminescence allows one to neglect non-radiative transitions, and the population of antibonding 1 Σ g + ground molecular state is usually considered as a main source of kinetic energy for a large-scale movement of atoms finishing in the Frenkel defects or desorption of atoms in the ground state -ground-state (GS) mechanism. On the other hand, the processes of formation of A-STE and M-STE centers themselves are accompanied by a considerable energy release to the crystal lattice, which also exceeds the binding energy ε b [6,11]. As in the case of solid Xe and Kr [6,7] the excited-state (ES) mechanism of M-STE to Frenkel pair conversion in solid Ar is supposed to occur by displacement of M-STE from centrosymmetric position in the <110> direction followed by reorientation to the <100> direction to stabilize the defect.…”

“…On the other hand, solid Ar and Ne have band-gap energies, E g , exceeding that of LiF and may be cited as the widest band-gap insulators. The excitonic mechanisms of subthreshold inelastic radiation-induced processes in solid Xe, Kr and Ne were studied recently [6][7][8][9][10]. In the present paper we include to overall picture of excitonically induced processes of large-scale atomic displacements in RGS the data on point defect formation in solid Ar following primary selective excitation by synchrotron radiation.…”

“…Rare-gas solids (RGS), or atomic cryocrystals, are the model systems in physics and chemistry of solids, and a lot of information about electronic excitations in RGS has been documented in several books and reviews [2][3][4][5][6]. As a consequence of the closed electronic shells, solid Xe, Kr, Ar, and Ne are the simplest known solids of the smallest binding energy, ε b , between atoms in the lattice.…”