Ion-Molecule Reactions below 1 K: Strong Enhancement of the Reaction Rate of the Ion-Dipole Reaction He++CH3F

Multipole-moment effects in ion–molecule reactions at low temperatures: part I – ion-dipole enhancement of the rate coefficients of the He+ + NH3 and He+ + ND3 reactions at collisional energies Ecoll/kB near 0 K

“…In a second step, we perform a convolution with a Gaussian distribution accounting for the collisionalenergy-dependent energy-resolution, as described in ref. 42, using the equation:…”

“…Advances in the experimental studies of ion-molecule reactions near 0 K have been recently made that rely on the use of laser-cooled and sympathetically cooled ions in ion traps and Coulomb crystals. 9,[37][38][39] Our own approach to study ionmolecule reactions at low energies consists of suppressing the stray-electric-field-induced heating of the ions by replacing the ion by an atom or molecule in a Rydberg state of high principal quantum number n. [40][41][42][43] In such states, the Rydberg electron moves on an orbit of large radius (pn 2 , e.g., E50 nm for n = 30), without significantly affecting the reactions involving the ion core. [44][45][46] The distant Rydberg electron, however, effectively shields the reaction from stray electric fields.…”

Deviation of the rate of the reaction from Langevin behaviour below 1 K, branching ratios for the and product channels, and product-kinetic-energy distributions

“…The Rydberg electron shields the reaction system from heating effects by stray electric fields. Moreover, the large dipole moments of Rydberg states enable the control of the motion of Rydberg atoms and molecules using Rydberg-Stark decelerators and deflectors [36][37][38][39][40][41], opening access to studies of ion-molecule reactions at very low collision energies in merged beams [42][43][44][45]. Recent studies based on this approach revealed pronounced enhancements of the reaction rate coefficients below 1 K in capture reactions resulting from the iondipole interaction in the He + + CH 3 F reaction [44] and from the ion-quadrupole interaction in the H + 2 + H 2 [42] reaction, but not in the H + 2 + HD [45] reaction.…”

“…Moreover, the large dipole moments of Rydberg states enable the control of the motion of Rydberg atoms and molecules using Rydberg-Stark decelerators and deflectors [36][37][38][39][40][41], opening access to studies of ion-molecule reactions at very low collision energies in merged beams [42][43][44][45]. Recent studies based on this approach revealed pronounced enhancements of the reaction rate coefficients below 1 K in capture reactions resulting from the iondipole interaction in the He + + CH 3 F reaction [44] and from the ion-quadrupole interaction in the H + 2 + H 2 [42] reaction, but not in the H + 2 + HD [45] reaction. In this article, we report on the study of the ionquadrupole interaction in the reaction between H + 2 and D 2 forming H 2 D + + D and HD + 2 + H and on the quantitative comparison of the collision-energy dependence of the reaction rate coefficient with that of the H + 2 + H 2 reaction forming H +…”

Quantum-state-dependent decay rates of electrostatically trapped Rydberg NO molecules

“…For example, they can be employed to study ionmolecule reactions, as most recently demonstrated in the case of the H + 2 + HD → H 2 D + + H reaction, at temperatures as low as 50 mK. [7][8][9][10] In this setting the Rydberg electron shields the reaction centre from stray electric fields that would otherwise cause heating. Long-lived Rydberg states of small molecules also offer opportunities for studies of low-energy molecular scattering that are dominated at long range by resonant dipole-dipole interactions, 11 and the exploration of the chemistry associated with ultra-long range Rydberg molecules, 12 formed of a Rydberg atom or molecule bound to a ground-state atom or molecule through low-energy Rydberg-electron scattering.…”