Stereodynamical Control of D 3 + Formation from the Bimolecular Photoreaction in the D 2 -D 2 Dimer.

We report the stereodynamic control of D 3 + formation from the laser-induced bimolecular reaction in a weakly bound D 2 -D 2 dimer via impulsive molecular alignment. Using a linearly polarized moderately intense femtosecond pump pulse, the D 2 molecules in the dimer were prealigned prior to the bimolecular reaction triggered by a delayed probe pulse. The rotationally excited D 2 in the dimer was observed to rotate freely as if it were a monomer. It was demonstrated that the yield of photoreaction product D 3 + is increased or decreased when the molecular axis of D 2 is parallel or perpendicular to the probe laser polarization, respectively. The underlying physics of this steric effect is the alignment-dependent bond cleavage of D 2 + in the dimer induced by a photon-coupled parallel transition.