Kinetic and Electronic Energy Dependence of the Reactions of Sc+ and Ti+ with D2O

Abstract

The reactions of Sc[sup +] and Ti[sup +] with D[sub 2]O are studied as a function of translational energy in a guided ion beam tandem mass spectrometer. Both ions react to form three ionic products. MD[sup +], MO[sup +], and MOD[sup +]. MO[sup +] formation occurs exothermically by dehydrogenation of D[sub 2]O, even though this reaction is spin forbidden for reaction of ground state M[sup 1] in both systems. In the titanium system, the effect of electronic energy on product formation is probed by varying the conditions used for forming Ti[sup +]. The a[sup 2]F state of Ti[sup +] reacts much more efficiently than the a[sup 4]F ground state at forming all three product ions. The relative reaction efficiencies are consistent with a recent study of the reverse reactions of MO[sup +] + D[sub 2]. State-specific cross sections and the competition between the various products indicate that the reactions occur primarily through a low-spin state of a D-M[sup +]-OD intermediate. Thresholds of the cross sections for endothermic formation of all three product ions are consistent with values calculated by using previously measured bond energies. 44 refs., 5 figs., 3 tabs.