Ion-molecule reactions within methane clusters initiated by photoionization

Photoionization experiments using light from the Berlin synchrotron facility BESSY were performed with methane clusters. A number of ionic reaction products with masses m = k + 16n (k = 16, 17, 28, 29, 31, 40 and 57 and n greater than or equal to 0) were determined . These are interpreted as series of cluster ions of the form (X x (CH/sub 4/)/sub n/) with X = CH/sub 4/, CH/sub 5/, C/sub 2/H/sub 4/, C/sub 2/H/sub 5/, C/sub 2/H/sub 7/, Ar, and Ar x CH/sub 5/. For all series except two (X = C/sub 2/H/sub 4/, C/sub 2/H/sub 7/) analogue ion-molecule reactions in the gas phase were observed. The occurrence of these two exceptions is believed to be caused by the cluster environment which contains the reagents for much longer time than that observed in gas-phase reactions. Some of the reactions (X = CH/sub 5/, C/sub 2/H/sub 5/, Ar, Ar x CH/sub 5/) exhibit Ar interband transitions, which are believed to originate from neutral precursor clusters with an abundance of Ar atoms. Possible reactions schemes are discussed and compared with the analogue ion-molecule reactions in the gas phase.