Stabilization of cluster dimers by centrifugal effects (vol 41, pg 195, 1997)

The influence of finite angular momentum on the stabilization of an (Ar13)2 cluster dimer in Ar13+Ar13 collisions is investigated with simulations and simple models. Local optimizations on the effective rovibrational potential-energy surface show that the centrifugal effects favor the mechanical stability of strongly prolate shapes. Molecular dynamics simulations are performed to study the collisions between two Ar13 subclusters. At low collisional energy and large impact parameter, trapping of the product cluster in its dimer-like configuration is found. For larger values of the angular momentum, the "molecular" cluster is found to remain in this dimer-like structure during the time of the simulation. Intermediate values of the angular momentum allow isomerization into more compact structures, but still dimer-like. Again, the final product appears as dynamically stable. All of these dimer-like products have the thermodynamical properties of a rotating rigid-like body. At high energy, unimolecular evaporation rates from collisional heating are calculated and comparisons with the predictions of the Rice, Ramsperger, Kassel (RRK) and Weisskopf models are discussed. Qualitative agreement with the simulations, in particular concerning the evolution of the rates versus angular momentum is found. The rates decrease when angular momentum is increased, especially when the total energy is low. Thus, the enhancement of the stability of the product cluster by centrifugal effects has also a statistical character. © Springer-Verlag 1997.