Comparison of near-threshold reactivity of ground-state and spin-orbit excited chlorine atoms with methane

Relative abundances of the various ionic charges resulting from photoionization of argon by monochromatked synchrotron radiation at energies between 3150 and 4900 eV have been measured with low statistical error. Despite the fact that already, right at the onset of K excitation (3203.5 eV), almost the full Is binding energy is deposited in the atom, the relative abundances change smoothly over the region of np excitation up to 6 eV above the limit. While this behaviour, caused by Rydberg shake-off (about 0.5 probability at the Is -4p resonance) and by recapture ofthephotoelectron via post-collision interaction, appeanta be undentoodthereinnoexplanation foragradualchange of relative abundances extending over tens of eV below the lowest K excitation. K + M and K + L single photon double excitations both show up as a smooth rise of the average ionic charge c j from the respective threshold to a plateau at considerably higher energy, the overall increase of being 0.206+0.02 and 0.13*0.01.

CS 2 and OCS molecules were excited and fragmented by x-rays of variable energy around the sulphur 1s threshold (2478 eV). Coincident detection of three ionic fragments by a time-of-flight mass spectrometer enabled the determination of branching ratios for 18 dissociation channels with total ionic charges between 2 and 7. While the electronic de-excitation is similar in both molecules (see the preceding paper), the dissociation shows differences, notably a more asymmetric distribution of charge onto the fragments of OCS. Branching among channels of the same total charge is independent of photon energy although the dominant de-excitation cascades are not. This is interpreted as an indication of strong interchannel mixing. A simple, parameter-free Coulomb explosion model to simulate the dissociative kinematics is described. Detailed results based on this model give, contrary to opinions to be found in the literature, very good agreement with observed momentum correlations whereas maximum kinetic energies are somewhat overestimated for channels of higher total charge.

Auger satellites arising from transitions in the presena of 'spectator' vacancies have minor intensity in electron impact excited spedra. They are, however, very efficiently produced if preceded by another Auger transition. We have measured the L -M M Auger spectrum of argon emitted after photoexcitation with broad-hand synchrotron radiation of energies largely lying above the K-shell ionization potential. The spstrum exhibits a high degree of line overlap and is shown to be a superposition of at least six L3-MM spedra belonging to various configurations of spectator vacancies and having comparable overall intensities. We made relativistic calculations in configuration average which reproduce the general appearance of the complex spectrum quite well. A number of lines in the L&4-MzMZr[LI and LZ&M&MZrM2,[M:] spectra have been analysed and 6ve L;' M;* states have been energetically located.

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