Anisotropy ofK39binding inC8K 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 ${\mathrm{C}}_8$K. The bremsstrahlung was obtained using an electron beam with $E_e$=8.5 MeV. The scattered intensities from the 5.262- and 6.334-MeV levels in ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ and from the 4.439-MeV level in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ were found to be dependent on the c-axis orientation of ${\mathrm{C}}_8$K 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 ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ nuclear levels caused by the zero-point energies of the ${\mathrm{C}}_8$K 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 ${\mathrm{C}}_8$K.