Accelerator mass spectrometry studies of highly charged molecular ions

The existence of singly, doubly, and triply charged diatomic molecular ions (B{dollar}sbsp{lcub}2{rcub}{lcub}q+{rcub}{dollar}, SiF{dollar}sp{lcub}q+{rcub}{dollar}, AlO{dollar}sp{lcub}q+{rcub}{dollar}, and Al{dollar}sbsp{lcub}2{rcub}{lcub}q+{rcub}{dollar} for q = 1-3) was observed by using an Accelerator Mass Spectrometry (AMS) technique. The mean lifetimes of 3 MeV boron diatomic molecular ions were measured to be {dollar}tau(sp{lcub}10{rcub}rm Bsbsp{lcub}2{rcub}{lcub}1+{rcub}) = 200.1 pm 8.5 mu s, tau(sp{lcub}10{rcub}Bsp{lcub}11{rcub}Bsp{lcub}2+{rcub}) = 72.4 pm 2.4 mu s{dollar}, and {dollar}tau(sp{lcub}10{rcub}rm Bsbsp{lcub}2{rcub}{lcub}3+{rcub}) = 4.5 pm 0.1 mu s{dollar}. No isotopic effects on the mean lifetimes of boron diatomic molecules were observed for charge state 3+. Also, the mean lifetime of SiF{dollar}sp{lcub}3+{rcub}{dollar} was measured to be {dollar}tau(sp{lcub}28{rcub}rm Sisp{lcub}19{rcub}Fsp{lcub}3+{rcub}) = 21.4 pm 0.7 mu s{dollar}. Ab initio molecular orbital calculations of the potential energy curves of the ground and low-lying excited electronic states of B{dollar}sbsp{lcub}2{rcub}{lcub}3+{rcub}{dollar} and SiF{dollar}sp{lcub}3+{rcub}{dollar} ions have been performed using the QCISD(T) method. The ground states of B{dollar}sbsp{lcub}2{rcub}{lcub}3+{rcub}{dollar} and SiF{dollar}sp{lcub}3+{rcub}{dollar} were found to be unbound, leading to the conclusion that these ions exist in metastable states. Some electronic states were found to be weakly bound (0.2-5.0 eV dissociation energy). Collision-induced interaction cross sections were measured for the diatomic boron molecular ions incident on a nitrogen gas target by using a differentially pumped gas cell. The dissociation cross sections of B{dollar}sbsp{lcub}2{rcub}{lcub}q+{rcub}{dollar}, q = 1-3, were measured to be on the order of 10{dollar}sp{lcub}-15{rcub}{dollar} cm{dollar}sp2{dollar} in the energy range 1-7 MeV. The dissociation cross section was found to decrease with increasing ion charge state, and with increasing collision energy. The single-electron-loss cross section of B{dollar}sbsp{lcub}2{rcub}{lcub}1+{rcub}{dollar} was measured to be on the order of 10{dollar}sp{lcub}-16{rcub}{dollar} cm{dollar}sp2{dollar}, and the double-electron-loss cross section of B{dollar}sbsp{lcub}2{rcub}{lcub}1+{rcub}{dollar} was measured to be on the order of 10{dollar}sp{lcub}-19{rcub}{dollar} cm{dollar}sp2{dollar} for 3 MeV. The single-electron-capture cross section of B{dollar}sbsp{lcub}2{rcub}{lcub}2+{rcub}{dollar} was measured to be on the order of 10{dollar}sp{lcub}-20{rcub}{dollar} cm{dollar}sp2{dollar}. The cross sections were also measured for 3 MeV B{dollar}sbsp{lcub}2{rcub}{lcub}q+{rcub}{dollar} ions incident on an argon gas target to investigate target dependences. The result shows that in general the measured cross sections per nucleon are larger for the argon gas target. Finally, the dissociation cross sections of diatomic boron molecular ions, when colliding with a nitrogen target, were measured as a function of energy. The dissociation cross sections were found to decrease with both increasing charge state and increasing collision energy.