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Translational–rotational interaction in the dynamics and thermodynamics of a 2D atomic crystal with a molecular impurity

“…We would like to note that the dynamics of a diatomic impurity in a 2D monoatomic matrix on a substrate is more complicated than in a 3D matrix of cubic symmetry [2,5]. Indeed, due to the high symmetry of the surroundings in 3D systems, TRI leads only to an increase in the molecular momentum of inertia without changing the form of the kinetic energy operator.…”

“…In the case of the heavy impurity (e < 0) the local level falls within the gap (w loc < D), and a contribution from w loc to thermodynamic functions can be comparable with that from the rotational degrees of freedom. Thus, the main contribution to the free energy and heat capacity from the impurity subsystem consists of two terms of the form (9) with frequencies w 0 andw loc , being determined as two least roots of the equation The situation is more complicated, when the librational frequency is inside the continuous phonon spectrum near its bottom (w 0 > D) [2,11]. Since for the heavy impurity w loc < D, the contribution to the thermodynamic functions from the local excitations prevails over the contribution from the rotational degrees of freedom.…”

“…unlike three-dimensional systems where the powertype dependence takes place [2]. Such a result is due to the gap in the phonon spectrum of the 2D monoatomic crystal commensurate with the substrate [3,12].…”

“…For 2D monoatomic crystals containing molecular impurities the interaction between rotational degrees of freedom and matrix phonon excitations, so-called translational-rotational interaction (TRI) [1], is an important factor controlling the dynamics of the impurity molecules. Since an impurity in a 2D solution moves in the low symmetry potential, its dynamics appears to be substantially more complex than that in a 3D system [2]. This can appreciably affect all physical characteristics, in particular, low-temperature heat capacity, and also can lead to some effects not found in the 3D case.…”

“…Besides, for the substrates with a triangular lattice ( ) z 2 By virtue of positive definiteness of the form (8) the coefficients DI ẑ, > 0. As a result, TRI leads to an increase in impurity main moments of inertia, that is the molecule becomes effectively heavier.…”