Study ofBinp+ions formed in liquid-metal ion sources

We present the mass spectrum of ${\mathrm{Bi}}_{\mathrm{n}}$ ${\mathrm{}}^{\mathrm{p}+}$ ions formed by the liquid-metal ion-source technique and the energy distribution of some of these ions. In the mass spectrum the ${\mathrm{Bi}}_{\mathrm{n}}$ ${\mathrm{}}^{+}$ intensities exhibit an even-odd alternation and the ${\mathrm{Bi}}_{\mathrm{n}}$ ${\mathrm{}}^{3+}$ intensities a modulo-8 periodicity. These two characteristics are discussed and explained as due to maxima of stabilities which can be understood by using simple models. The ${\mathrm{Bi}}_{\mathrm{n}}$ ${\mathrm{}}^{+}$ energy distribution is a two-peak distribution whereas for ${\mathrm{Bi}}_{\mathrm{n}}$ ${\mathrm{}}^{3+}$ we observe only one peak. These features, already observed for other elements (Au, Sn, Ge), confirm the emission mechanisms proposed by the authors. In particular, one peak of the ${\mathrm{Bi}}_{\mathrm{n}}$ ${\mathrm{}}^{+}$ ions corresponds to the explosion of mother metastable particles at some distance from the tip surface after a decay deexcitation time τ estimated at about ${10}^{\mathrm{-}11}$ s.