QUANTUM-MECHANICAL SIMULATIONS OF INELASTIC-SCATTERING IN COLLISIONS OF LARGE CLUSTERS - AR+(H2O)(11)

An approach based on the Time-Dependent Self-Consistent Field (TDSCF) is used to carry out quantum calculations of inelastic atom scattering from large, highly anharmonic clusters. The computation is carried ou t for low-energy collisions of Ar with (H2O)(11), and all the vibratio nal modes of the cluster are included. The method treats the collider atom classically, but the dynamics of the interacting anharmonic modes of (H2O)(11) is handled quantum mechanically. The results provide ins ight into the collision physics of large systems having soft anharmoni c modes, and into the role of quantum effects in such cases. The main findings are the following: (a) Large differences are found between qu antum and classical results with regard to energy transfer into specif ic cluster modes. (b) Classical calculations wrongly predict efficient excitation of many stiff modes, including processes that are quantum- mechanically forbidden. (c) Single quantum excitations are the most im portant transitions at the collision energy used. (d) Atom-atom pair d istribution functions of (H2O)(11) after the collision show insignific ant differences from the corresponding precollision distribution funct ions. The results show that quantum calculations of collision dynamics of low-temperature anharmonic clusters are feasible, and also necessa ry in view of the prediction of significant quantum effects. (C) 1998 American Institute of Physics.