Single photon K^-2 and K^-1 K^-1 double core ionization in C₂H_2n (n=1-3), CO, and N₂ as a potential new tool for chemical analysis

M. Nakano, F. Penent, M. Tashiro, T. P. Grozdanov, M. Žitnik, S. Carniato, P. Selles, L. Andric, P. Lablanquie, J. Palaudoux, E. Shigemasa, H. Iwayama, Y. Hikosaka, K. Soejima, I. H. Suzuki, N. Kouchi, and K. Ito

Accepted Thursday Mar 7, 2013

We have observed single photon double K-shell photoionization in the C2H2n (n=1-3) hydrocarbon sequence and in N2 and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the K-2 process in these molecules are extended by the observations of a single-photon double photoionization with one core-hole created at each of the two neighboring atoms in the molecule (K-1K-1 process). In the C2H2n sequence, the spectroscopy of K-1K-1 states is much more sensitive to the bond length than conventional ESCA spectroscopy based on single K-shell ionization. The cross-section variation for single photon K-1K-1 double core ionization in the C2H2n sequence and in the isoelectronic C2H2, N2 and CO molecules, validates a knock-out mechanism in which a primary ionized 1s photoelectron ejects another 1s electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.