Effect of kinetic and electronic energy on the reactions of Ti + with H 2, HD, and D 2

Abstract

Reactions of atomic titanium ions with H 2, HD, and D 2 have been examined using guided ion beam tandem mass spectrometry. The a 4 F ground electronic state and the b 4 F first excited state of Ti + are very closely spaced, 0.11 eV, and this makes definitive determination of their relative reactivities difficult. Either both states react efficiently above their thermodynamic thresholds or the a 4 F state is fairly unreactive. In the reactions of these states with HD, formation of the metal hydride ion and the metal deuteride ion are nearly equal in the threshold region, which indicates a statistically behaved intermediate. Excited states of Ti + produced by electron impact also appear to react at their thermodynamic threshold with an efficiency about 4 times that of the 4 F states. With HD, these states react to form TiH + preferentially, indicating a direct reaction. These results complement those of other atomic transition metal ions and can be explained by using simple molecular orbital concepts. These data are analyzed to yield a 0 K bond dissociation energy for TiH + of 2.31 ± 0.11 eV (53.3 ± 2.5 kcal mol −1).