TIME-ORDERING EFFECTS IN K-SHELL EXCITATION OF 170 MEV NE-7- SINGLE EXCITATION( COLLIDING WITH GAS ATOMS )

The method of 0-degrees Auger spectroscopy was applied to measure stat e-selective K-shell excitation in Li-like Ne7+ incident with 170 MeV o n H-2, He, CH4, Ne, and Ar. The high-resolution technique allows for t he separate analysis of the states P-2(a) and P-2(b) whose dominant co mponents are 1s(2s2p3P)2P and 1s(2s2p1P)2P, respectively. The results are used to study time-ordering and interference effects in the proces s of single excitation. For the state ls (2s2p3P)2P it is found that t he phenomenon of Pauli blocking inhibits the loss of time ordering, wh ereas dealignment effects diminish interferences between first- and se cond-order mechanisms. The 1s(2s2p1P)2P state involves partial loss of time ordering; however, non-spin-flip rules recover sufficient time o rdering so that interference effects can be observed. The semiclassica l approximation is used up to second order to provide conclusive evide nce for the measured interference effects.