The Effect of the Molecular Dipole and Quadrupole moments on Ion-Molecule Reaction Rates near 0 K

We review the results of our recent experimental and theoretical studies gas-phase ion-molecule reactions involving He+ ion at low collision energies (Ecoll), in kB⋅(0 – 40) K range. To avoid heating ions by stray electric fields, are studied within orbit a Rydberg electron. reach down to ~0 employing merged-beam setup. In case molecule with dipole moment (e.g., ammonia), we observe strong enhancement measured reaction yield decreasing Ecoll. This is attributed rotational states which experience linear negative Stark shifts field ion. When has no but quadrupole N2), suppression total lowest energy. Our interpreted aid an adiabatic-channel model.