  The linearized problem of plasma oscillations in layer (particularly, in thin
films) in external longitudinal alternating electric field is solved
analytically. Specular - accommodative boundary conditions of electron
reflection from the plasma boundary are considered. Coefficients of continuous
and discrete spectra of the problem are found, and electron distribution
function on the plasma boundary and electric field are expressed in explicit
form. Absorption of energy of electric field in layer is calculated.
