Anisotropy of K39 binding in C8K studied by nuclear resonance photon scattering

A new technique employing nuclear resonance photon scattering of bremsstrahlung has been used for studying the anisotropic binding of K atoms in the first-stage intercalated compound C8K. The bremsstrahlung was obtained using an electron beam with Ee=8.5 MeV. The scattered intensities from the 5.262- and 6.334-MeV levels in K39 and from the 4.439-MeV level in C12 were found to be dependent on the c-axis orientation of C8K with respect to the photon beam in a nuclear self-absorption measurement. This behavior is interpreted in terms of the anisotropy in the Doppler broadenings of the K39 and C12 nuclear levels caused by the zero-point energies of the C8K vibrational modes along and perpendicular to the graphite basal planes. The measured anisotropy was found to be somewhat higher than that calculated from the known vibrational spectra in C8K.