The effective electron-nucleus Hamiltonian with distorted electron waves

The interaction of non-relativistic nucleons with relativistic electrons is expressed by the Hamiltonian expanded in a power series of the inverse nucleon mass keeping interaction terms up to second order in the coupling constant a and retaining up through terms of order M-3. The effective Hamiltonian, describing the interaction of the electron wave distorted by the nucleus with the nucleon is obtained. This Hamiltonian describes the distortion of electron waves and allows one to calculate its effect. Using this Hamiltonian for the description of (e, e'p) and (e, e'NN) reactions for medium and heavy nuclei, the off-shell transition matrix elements can be calculated.