Resonant coherent excitation (RCE) of C5+ has been observed with the loss electron yield produced by ionization of the projectiles, measured in the backward direction from a bulk Si crystal. At a resonance energy of 3.01 MeV/u for Si(100), the loss electron yield obtained from the difference between the electron yield for the C5+ and C6+ beams has been increased by a factor of 1.2-1.3 due to RCE from the ground state to the first excited state (n = 1 to 2) of C5+. The backward spectroscopy of loss electrons allows observations of RCE that is restricted within an extremely thin surface layer of the bulk crystals. In addition, the RCE-assisted electron loss process is of vital importance for precise understanding of the loss electron spectra from single crystal targets. (c) 2004 Elsevier B.V. All rights reserved.