IONIZATION AND DISSOCIATION OF DIATOMIC-MOLECULES IN INTENSE INFRARED-LASER FIELDS

We report the first observation of infrared multiphoton dissociation of a strongly bound diatomic molecule, HCl+. The dissociation is explained by a charge-resonance coupling of electronic states of the molecular ion HCl+. This coupling results in Stark shifts which depend on the internuclear separation thereby changing the molecular bonding. Using a barrier suppression model, we obtain good agreement with the observed dissociation threshold. We show the close relationship between barrier suppression and chaotic dissociation. We also report the first quantitative theoretical and experimental study of infrared multiphoton ionization of a small molecule, HCl. Based on tunnel ionization, we develop a molecular ionization model that incorporates both the large Stark shifts of the molecular ion and the associated large induced dipole moments. The model agrees with the experiment for the multiphoton ionization of HCI. It allows us to derive a general expression for the maximum intensity which can be applied to a neutral molecule without ionizing it.