ULTRAFAST OH PRODUCTION IN CLUSTERS CONTAINING N2O AND HI

The geometrical arrangement of reagents is an important factor influen cing chemical reactions in condensed phases and molecular clusters. In the present study, OH buildup times have been recorded upon photolysi s of (N2O)(m)(HI)(n) clusters in order to elucidate the role of the cl uster environment on the reaction mechanism. The buildup times were me asured for different molecular beam compositions (i.e., degrees of clu stering). The buildup time changed from less than or equal to 100 fs a t the lowest backing pressures (119 and 132 kPa) to 430 fs at 188 kPa. It is argued that at the lower backing pressures the OH derives prima rily from binary N2O-HI complexes. However, regardless of the cluster species involved, the fast OH buildup at the lowest backing pressures suggests a dominant direct oxygen abstraction mechanism rather than re action via a vibrationally excited intermediate such as HNNOdagger. (C ) 1997 American Institute of Physics.