Autoionization processes

In this paper we examined quantum aspects of special classical configurations of two-electron atoms. In the doubly excited regime, we found quantum states of helium that are localized along ID periodic orbits of the classical system. A comparison of the decay rates of such states obtained in one, two and three dimensional ab initio calculations allows us to conclude that the dimension of the accessible configuration space does matter for the quantitative description of the autoionization process of doubly excited Rydberg states of helium. Whilst ID models can lead to dramatically false predictions for the decay rates, the planar model allows for a quantitatively reliable reproduction of the exact life times. 

This type of energy exchange in an autoionization process may correspond with the behavior of a kicked rotator in classical mechanics, which is known to exhibit chaos. It would be worthwhile to consider an autoionization process of a simple diatomic molecule in its Rydberg states to understand experimentally the essential dynamics of a quantum system, whose classical counterpart exhibits chaos. 

In this context, it should be pointed out that an algebraic decay has also been numerically observed in classical Coulomb-type models of atomic autoionization processes by Blumel [141]. This might turn out to be relevant for Rydberg molecules, which also represent Coulomb-type systems. For the recent observation of algebraic decays in Rydberg atoms, see Ref. 142. 

A relaxation process will occur when a compound state of the system with large amplitude of a sparse subsystem component evolves so that the continuum component grows with time. We then say that the dynamic component of this state s wave function decays with time. Familiar examples of such relaxation processes are the a decay of nuclei, the radiative decay of atoms, atomic and molecular autoionization processes, and molecular predissociation. In all these cases a compound state of the physical system decays into a true continuum or into a quasicontinuum, the choice of the description of the dissipative subsystem depending solely on what boundary conditions are applied at large distances from the atom or molecule. The general theory of quantum mechanics leads to the conclusion that there is a set of features common to all compound states of a wide class of systems. For example, the shapes of many resonances are nearly the same, and the rates of decay of many different kinds of metastable states are of the same functional form. 

Besides Penning ionization, electron tunneling is also registered in other autoionization phenomena in atomic collisions. For example, if the ionization energy of the A atom exceeds the sum of the first two ionization energies of the B atom, then a collision between the A+ ion and the B atom may involve an autoionization process [24]... 

The most important implication of not being a good quantum number is that blue and red states are coupled by their slight overlap at the core. In the region below the classical ionization limit blue and red states of adjacent n do not cross as they do in H, but exhibit avoided crossings as a result of their being coupled. Above the classical ionization limit blue states, which would be perfectly stable in H, are coupled to degenerate red states, which are unbound, and ionization occurs rapidly compared to radiative decay. It is really an autoionization process in which the blue state is coupled to the red continuum state at the ionic core. 

The advances in this field are related with the development of the theory of configuration interaction between different excitation channels in nuclear physics including quantum superposition of states corresponding to different spatial locations for interpretation of resonances in nuclear scattering cross-section [7] related with the Fano configuration interaction theory for autoionization processes in atomic physics [8],... 

The pump-probe spectroscopic time-resolved study of autoionization processes in atoms and molecules uses an ultra-short (100-500 as) XUV pulses for the pump stage in conjunction with an intense (1012-1014 W/cm2), few-cycle IR pulse as probe. Traditional time-independent approaches are inadequate to interpret these kind of experiments. This is so because, on the... 

In (a) and (b) the 6p Rydberg electron takes part in the autoionization process. Therefore, these processes are participator or involved transitions. In (c), (d), and... 

Every aqueous solution contains hydronium (H30+) and hydroxide (OH-) ions as a result of the water autoionization process,... 

TNF PVK combination the corresponding values were 0.23 and 25 A° respectively. The invariance of 0 with increased TNF concentration is explained by assuming that 0 is determined by local processes within a TNF-PVK (monomer) complex. The increase in r0 is attributed to the extended nature of the electronic states which influence the autoionization process. 

The distinction between shape resonance and autoionization processes, on a theoretical level, is one of single-channel versus multi-channel characteristics15. On an experimental level, the situation is less clear. However, shape resonances tend to be very broad and to exhibit delayed onset whereas autoionization leads to highly asymmetric profiles which often exhibit window resonance behaviour. We will discuss some of these distinctions in Section IV.A.l, in which photoelectron spectroscopy of the halomethanes is described. 

Some general rules for the autoionization process are derived next. These rules are based on the following approximations. The spectral feature in which autoionization effects are manifested must be a single, well-resolved line associated with a well-characterized rovibronic level, for which the autoionization process can be described to a good approximation by a single predominant mechanism. The consequences of the breakdown of these approximations are discussed in Section 8.9. 

The observed autoionization width is the result of decay into several different continua. Therefore, it is useful for calculations to define a quantity, the partial autoionization width, in which the initial and final states of the autoionization process are defined perfectly. One can then describe the total width, the only experimentally observable autoionization width, by summing over all possible final states. The initial state is specified by 1, n, and v, the final state by 2, v+ of the resultant ion, and e of the ejected electron. The partial autoionization width can be expressed by the Golden Rule formula ... 

In conclusion, Table 8.2 shows that the strongest autoionization process is electronic autoionization for light molecules and spin-orbit autoionization for... 

In reality, one encounters overlapping multiple resonances interacting with multiple continua. The analytical expressions given here represent an idealized situation. Several examples involving interferences between different autoionization processes [for example, in H2, interference between rotational and vibrational autoionization (Fig. 8.12) in N2, interference between vibrational... 

Understanding the spur structure as a function of the electron energy, especially below 1 keV. What is the relative significance of ionization and autoionization processes What is the origin of the observed spin effects ... 

An additional process deserves attention in the interpretation of Auger spectra, especially if rare earth metals and compounds are considered. The high 4f density of states above the Fermi level in these materials gives rise to resonant transitions 4d 4f (Zimkina et al., 1967 Sugar, 1972), which can decay by autoionization processes. The electrons ejected in such direct recombination... 

---