Autoionization Widths

Since autoionization involves a nonradiative change in energy of the core ion, the ejected electron obtains its kinetic energy from the superexcited (autoion-ized) state by conversion of 

The first two types of interaction are peculiar to molecules. The last two also appear in atoms, but nuclear motion introduces a level of complexity beyond that of the atomic case. 

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  

The interaction H12 can often be factored into electronic and vibrational parts, as in the case of predissociation, but here it is the electronic part that has the continuous character. In some cases, the vibrational part is simply an overlap factor and 

---

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,... 

In the present discussion, the total autoionization width for Penning ionization of He M or for decay of the transient molecular autoionizing state of [HeM] is assumed to be divided into two components a dipole-dipole part and an electron exchange part. The maximum width possible is assumed to be the sum of the two components [142], that is. 

Ch. Jungen Yes, I would agree with Prof. Field that autoionization widths in the continuum, spectral perturbations at high n, and the... 

As mentioned in Section II.A, the Pgl process is ideal for the application of the optical model. This is clear in the classical and semiclassical Pgl theory,24,25 for which opacity and cross-section formulas are completely equivalent to those given earlier in this chapter. The quantal optical model is also rigorously related to the elastic component of the quantal Pgl theory. Miller49 has shown that T(r), identified in Pgl as the autoionization width of the excited electronic state, may be accurately obtained by a standard Born-Oppenheimer electronic structure calculation as... 

In spite of the fact that the spectra can be understood as two-photon ICE spectra, implying that there is no serious departure from the independent electron picture, the quantum defects and autoionization widths of these states... 

Fig. 23.11. Core scaling of autoionization rates of the Ba msns and msnd states as a function of the principal quantum number of the core. The nd states show increasing autoionization width with increasing core size, while the ns autoionization rates are independent of the core principal quantum number (from ref. 36).

Figure 5.10 The variation of the autoionization width of the helium nq = n2 = 2 resonances of even parity as a function of nuclear charge, Z. The three dashed lines show the widths for the 2p2 3P resonances that cannot autoionize nonrelativistically, short dashed line [J = 0), long dashed line (J = 1), and long-short dashed line (J = 2). The three solid lines show the width of the three resonances for which autoionization is nonrelativistically allowed for comparison. A logarithmic scale is used to highlight the Z-dependence.

The band contour depends not only on the temperature but also on Hund s coupling cases. Jungen (1980) has pointed out that the rotational structure becomes narrower as n increases due to a change from Hund s case (b) to case (d). This envelope-narrowing effect must not be construed as a variation of autoionization widths with effective quantum number n. Fortunately, doubleresonance techniques in the vacuum ultraviolet region are now able to isolate... 

To a good approximation, the vibrational wavefunctions of the two series, which converge to the same vibrational level of the 2n1//2 and 2n3/2 limits, are identical, leading to a Av = 0 propensity rule and a vibrational factor equal to unity. Finally, the autoionization width given by Eq. (8.4.7) is... 

The magnitude of the spin-orbit splitting of the ion-core state affects the autoionization width most importantly through the minimum value of n, not through the size of I. This result is not surprising, since the present treatment was based on case (c) basis functions, which are eigenfunctions of the spin-orbit Hamiltonian (i.e., which diagonalize the spin-orbit part of the total Hamiltonian). (See Lefebvre-Brion, et al, (1985) for a theoretical treatment of the HI spin-orbit autoionization.)... 

As regards the autoionization widths. Table 4.1 contains the CESE results and the results of two previous theoretical ones that were obtained at some level of approximation using real-energy methods [125, 126]. The experimental ones are the ones quoted in Ref. [125]. 

We point out that since the structure of the CESE-SSA is such that it requires well-defined mafrix elements and computations that are practical and economic, its first-principles implementation has been extended to prototypical cases, such as the determination of partial and total autoionization widths in series of high-lying DESs [120] and Section 9.4, and of partial widths with interchannel coupling for fhe predissociation of excimer molecules [121]. 

The orbiting and the classical and semiclassical impact parameter models have been used to interpret inelastic scattering data in chemiionization, the dependence of ionization cross-section on collision energy and electron energy spectra, in order to gain information about the potential curves, V and V, and the autoionization width, (/ ). 

P. Erman, A. Karawajcyk, E. Rachlew-Kallne, E. Mevel, R. Zerne, A. L Huillier, C.-G. Wahlstrom Autoionization width of the NO Rydberg-valence state complex in the 11—12eV region. Chem. Phys. Lett. 239, 6 (1995)... 

The coincidence 1E spectrum was found to be particularly sensitive to the potential parameters and Ae autoionization widths. A consistent fit of both the total and the coincidence E i spectrum was achieved. The dominant mechanism proved to be autoionization from the ionic potential. Structure in the latter could be assigned to formation of excited Bi2 , e.g. Bi2 (A flu) formed in the ionic well. In addition Br2" "(A) is formed in the covalent entrance channel and is trivially identifiable, like in photoelectron spectroscopy, from the corresponding... 

---