Theory of resonance properties of electrons localized at liquid helium surface

The problem of the shape of line of electron optical transition between bound states on liquid helium surface was solved in the framework of independent bosons model. The states are realized for instance, in potential of positively charged impurity on the substrate or in the field of the He+ ion located under the surface. Importance of liquid (crater) surface deformation relaxation processes under electron is pointed out. Adiabatic approximation, according to which the crater does not change during electron transition, is not always just. At low temperature appearance of two maxima in the absorption line is possible. It is shown that distant tails in the optical absorption line obey the universal (Urbach's rule) experimental dependence on electron transition energy