LOW-ENERGY CLUSTER ION-ATOM COLLISION - COLLISIONAL ENERGY-TRANSFER AND COMPLEX-FORMATION OF AR-N(+) WITH AR-36

The collision-induced reaction of Ar-n(+) (n=2-23) with Ar-36 was investigated at the collision energies of 0.2 and 2.0 eV. The product ions were Ar-n'(+), and (ArArn'-1+)-Ar-36 (n'<n). The absolute cross sections for the product formation were obtained as a function of the size of the parent cluster ion. The cross section for the formation of Ar-n'(+) (evaporation) increased rapidly with n in the n less than or equal to 9 range, and slowly above it; the cross section at n=23 was approximate to 180 Angstrom(2). On the other hand, the cross section for the (ArArn'-1+)-Ar-36 formation (fusion) started to rise at n=7 and increased slowly as n increases. In order to elucidate the reaction scheme, the molecular dynamics (MD) simulation based on the diatomics-in-molecules (DIM) method was performed. The reaction (evaporation and fusion) cross sections estimated from the simulation reproduced the observed ones within an accuracy of 15% at n=6, 13, and 19 at the collision energy of 0.2 eV. The following reaction scheme based on this simulation was found to explain the experimental results: collisional excitation of the parent cluster ion Ar-n(+) and subsequent unimolecular dissociation (evaporation), and formation of a collision complex (ArArn+)-Ar-36 and subsequent unimolecular dissociation (fusion). In addition, it was confirmed by the MD calculation that the fusion proceeded via perfectly inelastic collision and following evaporation in the 0.2 eV collision of Ar-10(+) with Ar-36.