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

TL;DR

This study demonstrates that highly rotationally excited SiO$^+$ ions significantly increase reaction rates in a hydrogen abstraction process, with experimental and theoretical evidence showing the coupling of rotational states to reaction dynamics.

Contribution

It introduces a method to prepare SiO$^+$ ions in extreme rotational states and shows how these states enhance chemical reactivity, revealing the underlying mechanism.

Findings

Super-rotor states of SiO$^+$ increase reaction rates.

Rotational excitation couples with the reaction coordinate.

Theoretical studies support experimental observations.

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$^+$ + H$_2$ $\rightarrow$ 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 $\it{(j)}$ 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.