Dynamical quenching of laser-induced dissociations of diatomic molecules in intense infrared fields: Effects of molecular rotations and misalignments

The dynamical dissociation quenching (DDQ) effect is a new mechanism for la ser-induced vibrational trapping of molecules in the infrared (IR) spectral range. Previously demonstrated for one-dimensional, prealigned diatomic mo lecules [see F. Chateauneuf, T. Nguyen-Dang, N. Ouellet, and O. Atabek, J. Chem. Phys. 108, 3974 (1998)], the effect was shown to result from a proper synchronization of the molecular motions with the oscillations of the lase r electric field. The present paper explores the influence of rotations and misalignment of the molecular system on the DDQ effect. To this end, the t wo-dimensional (radial and angular) wave-packet dynamics of the H-2(+) and HD+ molecular ions are considered in an intense IR laser field starting fro m two types of initial angular distributions: The first type of distributio ns is appropriate for a field-free, pure angular momentum eigenstate and de notes typically an initially nonaligned, nonoriented molecule. The second t ype denotes a more or less well aligned and/or oriented initial condition, and is described by an angular width Delta which is considered a parameter in terms of which the efficiency of the DDQ effect are monitored. We demons trate that the DDQ effect remains efficient whenever a proper compromise is achieved between angular localization and angular-momentum (action) minimi zation. From the detailed analysis of the time-resolved dynamics, a time sc ale is also estimated for the molecule-field synchronization process which underlies the DDQ effect. An ultrafast laser-induced rotational-electronic energy transfer is found to compete with the DDQ effect, in the case the in itial rotational state denotes an almost perfect alignment and/or orientati on situation. (C) 2001 American Institute of Physics.