Enhancing reactivity of SiO+ ions by controlled excitation to extreme rotational states

Abstract

Optical pumping of molecules provides unique opportunities for control of chemical reactions at a wide range of rotational energies. This work reports a chemical reaction with extreme rotational excitation of a reactant and its kinetic characterization. We investigate the chemical reactivity for the hydrogen abstraction reaction SiO+ + H2 → SiOH+ + H in an ion trap. The SiO+ cations are prepared in a narrow rotational state distribution, including super-rotor states with rotational quantum number (j) as high as 170, using a broad-band optical pumping method. We show that the super-rotor states of SiO+ substantially enhance the reaction rate, a trend reproduced by complementary theoretical studies. We reveal the mechanism for the rotational enhancement of the reactivity to be a strong coupling of the SiO+ rotational mode with the reaction coordinate at the transition state on the dominant dynamical pathway.

Non-IRC Mechanism of Bimolecular Reactions with Submerged Barriers: A Case Study of Si+ + H2O Reaction

“…■ METHODS AND COMPUTATIONAL DETAILS Potential Energy Surface. The previous PES 18 covered Si + + H 2 O channel, but its long-range interaction was not accurately described, so we made some corrections. The modified PES used in this study consists of a short-range (SR) term for the strongly interaction region and a long-range (LR) term in the reactant asymptote.…”

“…Recently, we reported a high-level full-dimensional potential energy surface (PES) of the SiOH 2 + system for the SiO + + H 2 reaction. 18 The high fidelity fit to about 20,000 high-level ab initio points at the explicitly correlated unrestricted coupled cluster single, double, and perturbative triple levels with the explicitly correlated correlation-consistent polarized core− valence triple-ζ basis set (UCCSD(T)-F12b/pCVTZ-F12) 19,20 was achieved using a permutation-invariant polynomial neural network (PIP-NN) method. 21 The PES is obviously also suitable to investigate the Si + + H 2 O reaction, as it covers three reaction channels: SiO + + H 2 , SiOH + + H, and SiO + + H 2 .…”