Interaction of dislocations with point defects in solid parahydrogen

The rotational energy levels of single ortho impurities and a paired ortho cluster in the field of elastic displacements of a dislocation in solid parahydrogen are calculated microscopically. The lowering of the ground state is treated as the energy of the interaction of the ortho defect with the dislocation. At long distances it decreases in proportion to r−1. The values calculated within the framework of the theory of elasticity for the strengths of the interaction of an ortho single with an edge dislocation and a screw dislocation, respectively, are U = 0.39 K and U = 1.04 K. The energy of the ortho single at the dislocation core was calculated numerically on a computer and was found to be E = 0.78 and 0.92 K for an edge dislocation and a screw dislocation, respectively. At large separations (where the theory of elasticity is valid) the interaction strength of a paired ortho cluster is of the same order of magnitude of an ortho single. However, some ortho clusters break apart in passing through the dislocation core; their energy is in the form of a step of height 3.4 K. Such clusters constitute a new type of point defects. The interaction constants for the interaction of ortho impurities with dislocations are compared with the analogous constants for isotopic impurities. Numerical estimates give values of 5 and 9 K, respectively, for HD and D2 impurities.

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