Autoionizing resonances

C. A. Nicolaides, Theoretical approach to the calculation of energies and widths of resonant (Autoionizing) states in many-electron atoms, Phys Rev. A 6 (1972) 2078. 

The inner-shell hole 4d, produced by photoexcitation is filled by a non-radiative transition (radiative decay is negligible). Therefore, the resonance has a certain mean lifetime t which corresponds to a natural width T of approximately 114 meV for the xenon 4d5/2 -> 6p resonance. Autoionization produces many final ionic states, and the important branches are given by... 

However, it is often necessary to consider off-diagonal interactions between different partial waves. Recall (see Section 8.1.1) that, to first approximation, the vibrational photoionization intensities for direct photoionization are proportional to the Franck-Condon factors (e.g. (wx wx) ) between the initial state vibrational level (e.g. CO X1E+ux) and the v+ =0,1,2,... vibrational levels of the photo-ion electronic state (e.g., CO+ X2S+ u ). For electronic autoionization, the final state vibrational branching fractions are proportional to the Franck-Condon factors (e.g. ( x luA2)) between the resonant autoion-ized vibrational states (e.g. CO+, A2n, vj) and the final photo-ion state (e.g., CO+,X2S+ w+) (Smith, 1970). 

As it is clear from the aforementioned reviews, following the creation of QM fhere were only a few and sporadic contributions to elements of the physics of resonance (autoionizing) states in atoms until the early 1960s. Indeed, the systematic research activity concerning the theory and experiment on resonance states in atoms and molecules started in the early 1960s. 

Keywords Complex basis function method Slater-type orbital Gaussian-type orbital Least squares fitting Feshbach resonance Autoionization... 

The vibrational progressions can be adequately simulated through the calculation of Franck-Condon factors however the observed spin-orbit branching ratio, along with the intensity distribution, reflects a considerable contribution from both spin-orbit and field-induced resonant autoionization processes. Also, accidental resonances at the two-photon level with ion-pair states further perturb the distribution of peak intensities. 

It is well known that the value of the p parameter, more than the cross-section a, often shows a strong response to resonant structure embedded in the continuum. Given the sensitivity exhibited by the parameter in the foregoing there must be an a priori expectation that it would also show a strong response to resonant behavior. Computational methods do not yet exist to deal with autoionization phenomena in the systems of interest here, but one electron shape resonances can, in principle, be examined. 

From the available evidence Stener and co-workers [53, 60] conclude that the chiral parameter is more sensitive to small asymmetries in the molecular potential than to continuum collapse effects at resonance. At present, such conclusions must be provisional as there is little direct evidence. There is also no evidence regarding likely behavior at autoionization resonances, and this too deserves attention. 

As discussed in (4), the K-matrix has a pole at energies near a resonance and this yields a convenient method for the analysis of the narrow autoionizing states. The matrix representation of equation [2] upon a finite basis may be in fact recast in the form (4)... 

Bryant, G. P., Yiang, Y., and Grant, E. R. (1992), Triple-Resonance Spectroscopy of the Higher Excited States of N02. Trends in the Mode Dependence of Vibrational Autoionization via Asymmetric Stretch versus Symmetric Stretch and Bend, J. Chem. Phys. 96,4827. 

For collisions involving fast electrons, most of the relevant reactions given by Eqs. (9.1)-(9.13) occur with the primary and secondary electrons leaving the target molecule promptly, in about 10 sec. One the other hand, autoionization and dissociative ionization channels can result in a secondary electron being delayed relative to the primary, and in the case of resonant electron attachment, there may be a measurable delay in the exit of the primary electron. These processes are described in considerable detail by Mark et al. [19]. 

An interesting approach [62,63] to this problem, the use of 02 instead of 02, further substantiated the electron attachment to vdW molecules. For the BB mechanism, the isotope effect may be expected to appear as a change in the rates of initial attachment and autoionization channels, which are caused by a decrease of the resonance energy for 2 in comparison with 02. 

A elassieal expression for the eross seetion for eollisional de-excitation of He(2 P) is also derived from the formula by Eq. (16). However, the autoionization widths r R) for Penning ionization by resonant atoms are not identical to the empirical form of Eq. (18) for electron exchange. Instead, a direct transition due to a dipole-dipole interaction is proposed to govern this Penning ionization [126,139,140,143], that is,... 

Dissociative electron attachment (DEA) occurs when the molecular transient anion state is dissociative in the Franck-Condon (FC) region, the localization time is of the order of or larger than the time required for dissociation along a particular nuclear coordinate, and one of the resulting fragments has positive electron affinity. In this case, a stable atomic or molecular anion is formed along with one or more neutral species. Dissociative electron attachment usually occurs via the formation of core-excited resonances since these possess sufficiently long lifetimes to allow for dissociation of the anion before autoionization. 

The third line describes oscillation of a wave packet in an anharmonic potential (phase term omitted). Eq. (1) would be valid also in the presence of an intermediate resonance. In Eq. (2), the Apl dependence is only in the Plon terms. The fundamental arises from the sin terms (hence from dPion/dx) and the overtone from the sin2 terms. A phase jump of the fundamental is expected at a Tpr where dPlnn/dx and hence dPloir/dIE change sign. From these derivatives (proportional to the fundamental amplitude in Fig. 3) we can infer that Ploa has a maximum at 680 nm and a minimum near 405 nm. The maximum could reflect either an intermediate resonance or a two-photon resonance with an autoionizing state. The minimum is likely to announce a further rise of PIon at shorter Apr due to the lower order of ionization. 

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