Influence of Autoionization on ZEKE Peak Intensities

As noted in Section 8.1.2, numerous intensity anomalies are observed in ZEKE spectra. Most of them are due to autoionization. For the effects of rotational, vibrational, and electronic autoionizations, we refer to the work of Merkt and 

Softley (1993). Here we will analyze the effect of spin-orbit autoionization on ZEKE line intensities, for the example of HC1, where the ion-core ground state is a 2IIt state. 

In photoionization, the final states correspond to the ionization continua of the ion state, i.e. states consisting of an ion plus an electron. In the case of 

If the initial state in a photoionization transition is the X1E+ ground state, the transition moments into the continuum states are  

The transition intensities at the X2n1 /2 and X2n3/2 thresholds are equal, if the ion-core is at the Hund s case (a) limit. Experimentally, in conventional photoelectron spectra from the X1E+ ground state of HC1, the intensity ratio 2n1/2/2n3/2 is equal to 1.06 0.05 (Yencha, et al., 1989). This slight deviation from 1 can be explained because the 2n state is intermediate between Hund s cases (a) and (b) (Wang and McKoy, 1991). 

---