White lines in x-ray absorption

A quantitative discussion of the white line at the ${L}_{3}$ edge of platinum and its absence at the ${L}_{2}$ edge in x-ray absorption is presented. The predominance of ${d}_{\frac{5}{2}}$ character in the hole in the atomic $5d$ shell of Pt is shown to persist in the unoccupied portion of the $d$ band of the metal. The total weight in the ${L}_{3}$-edge white line is calculated and found consistent with the experimental value. A brief presentation of some experimental results is given including some suggestion of the range of validity of the sudden approximation in x-ray absorption.