The field-ionization of near-dissociation ion-pair states of I_2

摘要

Using a resonant multiphoton excitation pathway, it is shown that electronic states down to 30 cm~(-1) below the first ion-pair dissociation threshold of I_2 can be efficiently converted from initially prepared well-defined low-J states to long-lived (tau_d > 4 mus), subthreshold zero ion kinetic energy (ZIKE) ion-pair states which are analogous to high, zero electron kinetic energy, Rydberg states. A pulsed electric field is used to dissociate the ZIKE states and produce free-ion pairs (i.e., I~+ + I~-). Direct excitation to very high vibrational levels of the ion-pair states is ruled out and polarization data are used to probe the spectroscopic character of the doorway states to free-ion formation. The ion-pair dissociation limit, determined from the extrapolation to zero field of the onset of the prompt I~+/I~- signal, agrees well with the literature value.