Cold ion chemistry within a Rydberg-electron orbit: Test of the spectator role of the Rydberg electron in the $\textrm{He}(n) + \textrm{CO} \rightarrow \textrm{C}(n^\prime) + \textrm{O} + \textrm{He}$ reaction

Abstract Recently, a new method has been introduced to study ion-molecule reactions at very low collision energies, down below k B ? 1 K (Allmendinger et al 2016 ChemPhysChem 17 3596). To eliminate the acceleration of ions by stray electric fields in reaction volume, are observed within orbit Rydberg electron with large principal quantum number n > 20. This is assumed not influence taking place between ion core and neutral molecules. assumption tested here example He( ) + CO ? C( ?) O He reaction, which expected be equivalent C using merged-beam approach enabling measurements relative rates for energies E coll range from 0 about 25 collision-energy resolution ? 200 mK = 0. In contrast other studied so far this method, atomic product (C its electronic ground state does have rotational vibrational degrees freedom that corresponding [C( ?)] cannot decay autoionization. Consequently, one can investigate whether effectively conserved, as would spectator Rydberg-electron model. We measure distribution numbers reactant atoms pulsed-field ionization following initial preparation states values 30 45 observe conserved during reaction. observation indicates affected we conclude it affect either. conclusion strengthened collision-energy-dependent yields 30, 35 40, exhibit same behavior, i.e. marked decrease ? 5 K.