On the propagation of surface electromagnetic waves, similar to Rayleigh waves in the case the Leontovich boundary conditions

Let $\Sigma$ be a surface, which is a boundary of a domain containing electromagnetic wave field. We assume, that Leontovich boundary conditions take place on $\Sigma$. Surface waves (an electromagnetic version of classical Rayleigh surface waves in elasiticy theory) can exists, only if the coefficient in the Leontovich boundary conditions is pure imaginary. The ray theory of surface electromagnetic waves is developed in this paper.