RESONANT COHERENT EXCITATION OF FAST HYDROGEN-ATOMS IN FRONT OF A LIF(001) SURFACE

We have scattered protons and hydrogen atoms with energies of some keV from a LiF(001) surface under a grazing angle of incidence. From the intensity of Lyman-cr radiation (transition from n = 2 to n = 1, lambd a = 121.6 nm) as a function of projectile energy for different azimuth al orientations of the crystal surface, we find clear evidence for a r esonant coherent excitation of n = 2 states of hydrogen atoms in the o scillating electric field in front of the insulator surface.