X-ray specular reflectivity and anomalous scattering in the vicinity of the SiKabsorption edge in quartz

X-ray specular reflectivity of quartz has been measured at various grazing angles as a function of the frequency in the vicinity of the $K$-absorption edge of silicon. An anomalous behavior in the spectral distribution of the continuous reflected intensity is observed accompanying a maximum in the photoabsorption spectrum. The optical constants are deduced from the measured reflectivity coefficients. We present a simple theoretical approach which enables us to account for the experimental results.