TY - JOUR AU - Zhelyazkova, Valentina PY - 2022/04/27 Y2 - 2024/03/29 TI - The Effect of the Molecular Dipole and Quadrupole moments on Ion-Molecule Reaction Rates near 0 K JF - CHIMIA JA - Chimia VL - 76 IS - 4 SE - Scientific Articles DO - 10.2533/chimia.2022.316 UR - https://www.chimia.ch/chimia/article/view/2022_316 SP - 316-321 AB - <p>We review the results of our recent experimental and theoretical studies of gas-phase ion-molecule reactions involving the He<sup>+ </sup>ion at low collision energies (<em>E<sub>coll</sub></em>), in the k<sub>B</sub>⋅(0 – 40) K range. To avoid heating of the ions by stray electric fields, the reactions are studied within the orbit of a Rydberg electron. We reach collision energies down to ~0 K by employing a merged-beam setup. In the case of a molecule with a dipole moment (e.g., ammonia), we observe a strong enhancement of the measured reaction yield with decreasing <em>E<sub>coll</sub></em>. This enhancement is attributed to rotational states which experience linear negative Stark shifts in the electric field of the ion. When the molecule has no dipole moment but a negative quadrupole moment (e.g., N<sub>2</sub>), we observe a suppression of the total reaction yield at the lowest collision energy. Our results are interpreted with the aid of an adiabatic-channel model.</p> ER -