Nonadiabatic effects in the photoelectron spectra of HCl and DCl. II. Theory

The vibrationally resolved photoelectron spectra of HCl and DCl in the 25--28 eV region were computed using a time-dependent approach for the nuclear dynamics. The spectral features cannot be understood without including a nonadiabatic coupling between the dissociative 3²Σ⁺ state and the bound 4²Σ⁺ state in the adiabatic picture. Alternatively, in the diabatic picture a dissociative two-hole--one-particle state interacts with a bound one-hole state. The molecular system is of intermediate coupling strength, i.e., it cannot be described by a single potential-energy curve. The interaction between a bound and a dissociative state leads to Fano resonances superimposed on a broad background, as observed in the experimental spectra [Burmeister et al., Phys. Rev. A 64, 012704 (2001)]. From modified potential-energy curves, all features of the experimental spectra, including Fano resonance parameters and lifetimes, were reproduced. From the simulations we observe that two additional peaks in the experimental DCl spectra should appear if the resolution were to be enhanced to around 10 meV.