METASTABLE FRAGMENTATION OF (C4H10)NC4H7-REACTIONS OF C4H7+( CLUSTER IONS INDUCED BY DELAYED ISOMERIZATION)

The metastable fragmentation of the cluster ions (C4H10)(n)C4H(q)+ (q = 7 to 10) produced by the electron impact ionization of a neutral n-b utane cluster beam has been studied with a double focusing sector fiel d mass spectrometer. For q > 7, the usual statistical single-monomer e vaporation is the only observable metastable fragmentation channel. Su rprisingly, the (C4H10)(n)C4H7+ cluster ions were found to exhibit a m ore complex metastable decay pattern, involving not only the single-mo nomer evaporation, but also two additional fragmentation channels lead ing to evaporation of 2 to 4 and 4 to 7 (C4H10) monomers, respectively . After studying the dependence of the parent and the fragment ion cur rents on the electron energy, we concluded that the C4H7+ ionic chromo phore of the (C4H10)(n)C4H7+ cluster ion is produced after internal H- transfer between n-C4H10 and some primary fragment ion (e.g., C2H5+, C2H3+, C3H3+, CH3+, C3H4+) of n-butane within the cluster. A mechanism based on the energy storage in metastable isomers of the C4H7+ chromo phore ion is suggested to explain the unusual metastable fragmentation pattern of (C4H10)(n)C4H7+ cluster ions.