Metastable decay of Ar+@B3produced by electron impact ionization of a supersonic Ar cluster beam has been investigated qualitatively and quantitatively with a double focusing sector field mass spectrometer. We present direct experimental proof that the observed metastable decay of Ar+ast;3into Ar+in the microsecond time regime proceeds predominantly via a sequential decay series Ar+@B3rarr;k3,2Ar+ast;2rarr;k2,1Ar+involving the evaporation of a single monomer in each of these successive decays. The metastable decay rates deduced are very different, i.e.,k3,2=45 sminus;1andk2,1=680 sminus;1at an ion acceleration voltage of 3 kV. Moreover, the metastable decay rates of Ar+@B3exhibit a strong dependence on time elapsed since electron impact production of the Ar+3, and on ion production parameters (i.e., size and internal excitation energy of the neutral precursor). For instance photodissociation (with visible laser light) of the neutral cluster beam leads to a dramatic increase of the observed metastable reaction rules yielding values of up to 100thinsp;000 3minus;1in the mgr;s time regime.
展开▼
