Angle-resolved and internuclear-separation-resolved measurements of the ionization rate of the B state of I_2 by strong laser fields

摘要

Angle-resolved and internuclear-separation-resolved measurements of the single ionization rate of neutral I_2have been obtained. By launching a wave packet in the B~3 П_u~+state(Bstate) of I_2with a 50-fs tunable pumppulse we can measure the ionization rate as a function of internuclear separation as the wave packet evolves in theB state. Moreover, since the ground to B-state optical transition dipole moment is parallel to the internuclear axis,the B-state subpopulation of the I_2thermal ensemble will have a high degree of alignment, allowing for angularmeasurements. The B state shows the well-known effect of enhanced ionization at a critical separation, R_c,withan enhancement factor of 22 when the ionizing field is polarized along the internuclear axis and the enhancedionization decreases when the angle between the field and the axis increases from 0° to 90° , finally disappearingat 90° . These results on the enhanced ionization of the B state of I_2give the most precise determination ofR_cfor any molecule and agree extremely well with the prediction from a simple model of electron localization.