Theory of EXAFS--Higher-Order Corrections and Teo's Multiple Scatteri11gs*)--

A theoretical method for obtaining formulae of the EXAFS is proposed on the basis of Lee's scheme. A general rule to describe matrix elements for any multiple scattering path is found in the.lowest-order approximation in l/kr~l, on the premise that excitation of the X-ray absorbing atom is limited to an s state; k is the wave number of ejected photoelectrons and r is the distance between two successive scatterings. Teo's EXAFS formula for the multiple scatterings over Teo's triangle can almost be re-produced by applying the above rule. However, the result does not exactly equal Teo's result but equals that of Boland, Crane and Baldeschwieler. Correction terms for the basic EXAFS formula with nearest-neighbor scatterings are given exactly to the order of (11 kr)'