THRESHOLD PHOTOELECTRON-SPECTROSCOPY OF HCL UP TO 40 EV

The threshold photoelectron spectrum of HCl has been recorded using synchrotron radiation over the energy range encompassing both outer and inner valence ionization, A large enhancement in the intensity of the v(+) = 0-1 bands of the HCl+2 Pi((3/2)) subsystem was observed in comparison with the same vibrational bands of the (2) Pi((1/2)) subsystem which are attributed to autoionization processes. Resonance autoionization was also found to be responsible for the populating of upper vibrational levels (v(+) = 2-14) of the X(2) Pi(i) system in the Franck-Condon gap region preceding the onset of the A(2) Sigma(+) band system. The observation of vibrational-band broadening for v(+) = 7-10 of the A(2) Sigma(+) system is attributed to combined autoionization processes between repulsive neutral Rydberg states and bound vibrational levels of the A(2) Sigma(+) state and the continuum of repulsive ion states, the latter of which are responsible for predissociation in the A(2) Sigma(+) State of HCl+. In the inner valence ionization region (20.0-40.0 eV), pronounced resonance structure was observed which correlates well with the calculated energy positions of 4 sigma(-1) satellite ions states of HCl+. In addition, the direct populating of repulsive ion states in the 20.0-25.2 eV range is suggested by the observation of several broad, structureless band features, and the detection of three vibrational bands in this same energy range suggests the presence of a bound neutral Rydberg state that undergoes autoionization into the continuum of a repulsive ion state.