Dynamics of the Oxygen Atom Transfer Reaction between Carbon Dioxide and the Tantalum Cation

Abstract

The understanding of fundamental atomic-level processes often requires well-defined model systems. The oxygen atom transfer from CO2 to a transition metal cation in the gas phase presents such a model system. We investigate the reaction of Ta+ + CO2 for which the formation of TaO+ is highly efficient and attributed to multistate reactivity. Here, we study the atomistic dynamics of the oxygen atom transfer reaction by recording experimental energy and angle differential cross sections by crossed beam velocity map imaging supported by ab initio quantum chemical calculations. Product ion velocity distributions are dominated by signatures for indirect dynamics, despite the reaction being highly exothermic. Product kinetic energy distributions show little dependence on additional collision energy even with only four atoms involved, which hints at dynamical trapping behind a submerged barrier.

Ta+ and Nb+ + CO2: intersystem crossing in ion–molecule reactions

“…The deep minimum of the post-reaction complex is reached which can be characterized by the coordination of a CO molecule to the niobium oxide cation NbO + . The minimum energy pathway for the oxygen atom transfer reaction for Ta + + CO 2 is given as comparison 15 in Fig. 1.…”

“…The angular distribution for reaction (2) is added as a grey line in Fig. 2c and d for comparable relative collision energies of 1.4 eV and 2.0 eV 15 for a direct comparison with the distribution for reaction (1). Both reactions show very similar angular distributions.…”

“…The experimental set-up has been described in detail previously. 15 Only a brief explanation will be given here. Ions are formed in a laser vaporization source 37,38 by focusing the 2 nd harmonic of a Nd:YAG laser (Innolas SpitLight, 532 nm, 20 Hz, ≈4 mJ per pulse) onto a rotating niobium target (Alfa Aesar, 99.97%).…”

“…32,33 The recent experiments were the first to take a look at the dynamics of the oxygen atom transfer reaction involving carbon dioxide. 15 The TaO + product was scattered predominantly isotropically at relative collision energies of up to 2 eV. The found indirect dynamics were surprising considering the limited number of states to dispose the available energy into.…”

“…Recently, some of the present authors applied another experimental approach to the Ta + + CO 2 reaction by recording energy and angle differential cross sections in a reactive scattering experiment in combination with high level ab initio calculations. 15 Differential cross sections give insight into the atomic level rearrangement during a reactive collision, thereby probing the dynamics of a reaction. 24–27 If experiments are carried out under single collision conditions, energy and (angular) momentum conservation allow us to extract information on the molecular rearrangement during the reactive collision from the product ion velocity distribution.…”