Modeling of the thermal migration mechanisms of atomic oxygen in Ar, Kr, and Xe crystals

Abstract

Accommodation and migration of the ground-state (2s22p4 3P) oxygen atom in the ideal Ar, Kr, and Xe rare gas crystals are investigated using the classical model. The model accounts for anisotropy of interaction between guest and host atoms, spin–orbit coupling, and lattice relaxation. Interstitial and substitutional accommodations are found to be the only thermodynamically stable sites for trapping atomic oxygen. Mixing of electronic states coupled to lattice distortions justifies that its long-range thermal migration follows the adiabatic ground-state potential energy surface. Search for the migration paths reveals a common direct mechanism for interstitial diffusion. Substitutional atoms are activated by the point lattice defects, whereas the direct guest–host exchange meets a higher activation barrier. These three low-energy migration mechanisms provide plausible interpretation for multiple migration activation thresholds observed in Kr and Xe free-standing crystals, confirmed by reasonable agreement between calculated and measured activation energies. An important effect of interaction anisotropy and a minor role of spin–orbit coupling are emphasized.

Trapping and thermal migration of the first- and second-row atoms in Ar, Kr and Xe crystals

“…[58][59][60] Thus, the present consideration should be related to a hypothetical case rather than to a description of the real F@RG systems. We should also note that the results for the O atom reported here practically coincide with those from our previous publication 35 with the marginal differences emerging from the use of more extended crystal models. In contrast, the extensive study performed here for the C atom resulted in more detailed characterization of the C@RG system than we achieved previously in ref.…”

“…Direct and indirect indications of the TIM were reported for the majority of the first-and second-row atoms, namely, for H, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Li, 20,21 B, 22,23 C, [24][25][26][27][28][29] N, [30][31][32][33][34] O (see ref. 35 and references therein) and F. [36][37][38][39][40][41][42] However, the TIM activation energies and rates were reliably determined in the selected RG matrices only for H [5][6][7]9,12,13,15 and O 31,…”

“…This extra degree of freedom significantly reduces all the activation barriers bringing them to remarkably better agreement with the experiment. 35 A subsequent model study related to carbon atoms indicated that the interaction anisotropy can even induce a critical phenomenon that drastically changes the structure of the IS site and related IS-IS migration pathway. 57 The main purpose of the present paper is to enhance the knowledge about TIM by modeling the interstitial light atoms in the fcc crystals of RG = Ar, Kr and Xe.…”

Infrared Spectroscopic Studies of Oxygen Atom Quantum Diffusion in Solid Parahydrogen

“…In more recent thermodynamic modeling studies of the thermal migration mechanisms of O( 3 P) atoms in noble gas crystals conducted by Buchachenko and co-workers, 81 the calculated barriers were significantly lower (807 cm −1 ) with activation energies (758 cm −1 ) only slightly higher than the experimentally determined values. In their paper, Buchachenko and co-workers comment that the earlier theoretical studies of Raff suffered from inaccurate description of the guest−host interaction potential where the anisotropy of the intermolecular interaction between the p-state oxygen atom and host atoms was not considered.…”

“…In their paper, Buchachenko and co-workers comment that the earlier theoretical studies of Raff suffered from inaccurate description of the guest−host interaction potential where the anisotropy of the intermolecular interaction between the p-state oxygen atom and host atoms was not considered. 81 Another issue in modeling the solid-state chemistry is that the matrix host must be allowed to relax around the guest species, and the coupling between the guest and the matrix host is very important when calculating the minimum energy pathways to model experiment. Modeling the diffusion in solid p-H 2 requires different theoretical approaches because solid p-H 2 is a quantum solid.…”