Competition between geometrical and dynamical squeezing during a Franck-Condon transition.

Abstract

The form of the molecular vibrational wave packet that is generated when a short laser pulse excites a Franck-Condon transition is examined. Particular attention is paid to the case when the vibrational potentials in the ground and excited electronic states have different characteristic frequencies and the exciting pulse duration is sufficiently long that the nuclei move during the excitation. It is shown that both the nonadiabatic change in vibrational frequency and the vibrational dynamics can cause squeezing of the resulting wave packet. For a pulse of sufficiently short duration, and for molecules in which the nuclei are more tightly bound in the excited electronic state, the dynamical squeezing dominates that arising from the change of vibrational frequency.