Multielectron X-Ray Photoexcitation Measurements in Krypton

X-ray photoabsorption measurements were carried out on krypton near the $1s$ ionization threshold, by use of synchrotron radiation. A rich, well resolved spectrum of simultaneous two- and three-electron excitations is detected. Feature identification is supported by both relativistic and nonrelativistic calculations. The data support in detail the $Z+1$ approximation for both two- and three-electron excitations. No indication of a preferred Coster-Kronig decay channel for $1s4s$ hole states is found, in contrast with argon. The partial cross sections are in good accord with shakeup theory and photoelectron data on other noble gases.