Photoinduced molecular dissociation and photoinduced recombination mediated by superfluid helium nanodroplets

We have investigated photoinduced chemical reaction dynamics of cold, isolated Cr 2 molecules in helium nanodroplets (He N ), exploiting the quantum state specific spatial separation of solvated and surface locations on the droplet. The molecules are excited to achieve dissociation to a ground state (a 7 S 3 ) and a metastable state (a 5 S 2 ) atom. State specific spatial separation, in combination with efficient translational cooling to avoid ejection, causes the ground state atom to be solvated inside the droplet while the metastable atom migrates to the surface. A barrier between the two reactants formed by the He N prevents recombination. We apply a resonance-enhanced multiphoton ionization scheme including the transition of the surface atom as well as a two-laser scheme including the transition of the solvated atom in order to verify the locations and separation of the dissociation products. Furthermore, ionization of the a 5 S 2 surface atom triggers solvation followed by geminate recombination with the a 7 S 3 atom, which is verified by the detection of Cr 2 + molecular ions. For small Cr clusters, our results indicate that they may be composed of chromium dimers that exhibit the same dissociation behavior. Photoinduced predissociation of Cr 2 in helium nanodroplets causes stable, quantum state specific spatial separation followed by geminate recombination upon photoionization.