The inner-shell excited states, (1s)-1(2pu)1,3u of carbon monoxide have been observed in electron impact excitation, as a function of incident energy via their decay, by electronic ejection, to an ionic state of the molecule. A shift in the energies of these ejected electrons has been observed and is explained in terms of a post-collision interaction effect. A detailed description of the apparatus is presented. The relative cross section for the formation of the CO+(B 2u) final ionic state, via the decay of these inner-shell excited states, is compared with predictions of a theoretical model.
The measuring (accepted) angular range of the double electron spectrometer of the Institute of Physics has been restricted in a rotatable manner. We have measured the electron spectra of the most important four autoionizing states of helium in four emission angular regions. The mathematical model of the autoionizing and scattered electron peaks of the spectra is shown in the paper. The Fano interference with the direct ionization background and energy spread of the primary electron beam have significant roles in this model.
In this work-on our way towards the experimental study of the state-to-state interference-we have dealt with the particular question of interference between the direct and indirect ionization of He by electron impact. The measured electron spectra include both the autoionizing and scattered electron peaks. The primary energy values were chosen in the neighbourhood of the critical energy of the interference between the 2s 2 (1 S) and 2p 2 (1 D) autoionizing resonances in such a way that the groups of the autoionizing electron peaks and the scattered electron peaks are well-separated and hereby their evaluation is more reliable. On the basis of a computer fitting procedure we have determined the parameters of the Fano-type peaks below and above the critical energy.
The electron impact excitation of the autoionizing states of helium, their subsequent decay into the same He + 1s -1 final ionic state, and the interference of these processes have been studied. We concentrated on the exchange interference of the 2s 2 ( 1 S) and 2p 2 ( 1 D) states in the 60°-120° scattering angular range. Our evaluation method is based on the comparison of spectra measured at around the critical primary energy (93.15 eV) and the synthetized ones. The peak parameters for the synthetized spectra are obtained from measurement done a few eV below or above the critical energy, where the scattered and ejected electron peaks are well separated. INTRODUCTIONInterference usually refers to the interaction of coherent waves that originate from the same source, but travel via two different paths. The state-to-state (exchange) interference can occur when a common final state originates from a common initial state via two different intermediate states. In an electron impact process, the common final state can take place at a unique (critical) electron impact energy, where the energy of the scattered electron from one reaction path equals the energy of the ejected (autoionizing) electron released along the other path and vice versa: in that case the scattered-ejected electron pairs are indistinguishable.In our work the intermediate states are the doubly excited autoionizing states of helium (2s 2 ( 1 S), 2s2p( 3 P), 2p 2 ( 1 D) and 2s2p( 1 P)) that decay into the same He + 1s -1 final ionic state. We concentrate the interference of the 2s 2 ( 1 S) and 2p 2 ( 1 D) resonances, where some resonance-like phenomena have been observed [1], [2], [3]. The excitation energies (ER) of these autoionizing states are 57.83 eV and 59.91 eV. The energy of their common He + 1s -1 final state is EF = 24.59 eV, hence the energies of the ejected autoionizing electrons (Ea=ER−EF) are 33.24 eV and 35.32 eV, respectively [9]. At E0=93.15 eV primary energy, the energy of the scattering peaks (Es=E0-ER) associated with the generation of these autoionizing states are 35.32 eV and 33.24 eV. Thus the ejected-scattered (scattered-ejected) electron pairs going along the two paths have the same energies (33.24; 35.32 eV); hereby the critical primary energy for this pair is 93.15 eV.The energy spectra measured at the critical energy are obviously complex, since the energies of at least two-two electron peaks coincide. In this example there is one coinciding scattered-ejected electron peak pair both at 33.24 eV and 35.32 eV, the other parameters of which, however, differ significantly. Moreover, the energy of the 2s2p( 1 P) peak only differs from that of the 2p 2 ( 1 D) peak by 0.23 eV (which our experimental equipment just cannot resolve), i.e. in our spectra there are two significantly overlapping peak triplets. We can hope to separate these, i.e. to fit the spectrum, only if we keep almost all of the parameters (which we have determined beforehand by performing measurements at another primary energy) of the peaks
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