Host-guest interactions of ferrocene in KY zeolite were investigated using muon spin relaxation (muSR). Temperature-dependent measurements enable us the determination of the activation parameters for the low energy dynamic processes of,the encapsulated ferrocene. A comparison between the pSR results and the earlier neutron measurements illustrates the advantage of the former technique for probing the lowest unoccupied molecular orbital (LUMO). (C) 2003 Elsevier B.V. All rights reserved.