Observation of site-specific decay processes in Ar-Kr mixed clusters following K-shell excitation of Kr

Multiple ion coincidence momentum imaging measurements have been performed for an Ar-Kr mixed rare-gas cluster with an average cluster size 〈N〉 = 100 in the 1s threshold region of Kr. The signals resulting due to the photoabsorption by Kr have been extracted on the basis of the difference in the spectra between 14.08 and 14.50 keV, i.e., on both sides of the 1s threshold for Kr. The time-of-flight spectra for the clusters reveal that multiply charged cluster ions produced as a result of inner-core excitation emit many singly charged ions such as Kr+, Ar+, ArKr+, and Ar2+. The abundance of daughter ions suggests the transfer of positive charges from the X-ray absorbing atom to the surrounding atoms before the Coulomb explosion is suggested from. The momentum of daughter ions is deduced from the time-of-flight and position data, and the momentum distribution shows the characteristic size dependence of the ions on the number of coincidence signals Ncoin, i.e., the average momentum of the Ar+ ions increases with Ncoin, while that of the Kr+ ions decreases. The Ncoin dependence of momentum is interpreted according to the site-dependent decay processes.