A recently developed method is used to make acoustic measurements of VSe2 single crystals. The components of the elastic constant tensor are determined from the data of these measurements. The experimental data are used to calculate the total and partial phonon densities of VSe2, which permit an explanation of the vibrational spectra of this compound.

The scattering of acoustic waves on a planar defect in the interior of a crystal is studied by the methods of lattice dynamics. The model chosen consists of two semi-infinite, highly anisotropic crystals, the forces of interaction between which are distinct from the interactions within the crystals themselves. The model is used to study the resonant transmission of waves through an impurity monolayer. This resonant transmission effect is due to the weak coupling of the defect to the host lattice and cannot be described in the framework of the standard theory of elasticity, since the displacements of the defect layer and of the closest-lying layers of the host matrix are substantially different. For nongrazing angles of incidence the resonant transmission effect can be illustrated qualitatively by the example of an infinite linear chain containing a point impurity.

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