Quantum state–resolved molecular dipolar collisions over four decades of energy

Abstract

Collisions between cold polar molecules represent a fascinating research frontier but have proven hard to probe experimentally. We report measurements of inelastic cross sections for collisions between nitric oxide (NO) and deuterated ammonia (ND 3 ) molecules at energies between 0.1 and 580 centimeter −1 , with full quantum state resolution. At energies below the ~100-centimeter −1 well depth of the interaction potential, we observed backward glories originating from peculiar U-turn trajectories. At energies below 0.2 centimeter −1 , we observed a breakdown of the Langevin capture model, which we interpreted in terms of a suppressed mutual polarization during the collision, effectively switching off the molecular dipole moments. Scattering calculations based on an ab initio NO-ND 3 potential energy surface revealed the crucial role of near-degenerate rotational levels with opposite parity in low-energy dipolar collisions.

A Century Ago the Stern–Gerlach Experiment Ruled Unequivocally in Favor of Quantum Mechanics

“…[102] The ensuing field of chemical reaction dynamics has remained one of the chief preoccupations of chemical/molecular physics to date. [103,104] While the refinement of mass-spectrometric techniques enabled conclusive elucidations of complex reaction mechanisms in the gas phase, [105,106] the development of soft desorption ionization beam methods (electrospray) [107] led to biological and medical applications of molecular beams. [108,109] Spectroscopy of molecular species loaded into or produced within superfluid helium nanodroplets [110][111][112] provided new incisive means to elucidate their structure, reactivity, and solvation.…”

Differential Cross Sections for Pair-Correlated Rotational Energy Transfer in NO(A2Σ+) + N2, CO, and O2: Signatures of Quenching Dynamics

“…In principle, Stark or other state-preparation techniques can also be applied to the collider beam, allowing inelastic collisions that are fully state-to-state in both collision partners. This clearly presents a significant additional experimental challenge but has very recently been demonstrated by Meerakker and co-workers in the NO­(X) + ND 3 system, where the Stark-decelerated NO­(X) collided with ND 3 that was Stark hexapole state-selected …”

“…This clearly presents a significant additional experimental challenge but has very recently been demonstrated by Meerakker and coworkers in the NO(X) + ND 3 system, where the Starkdecelerated NO(X) collided with ND 3 that was Stark hexapole state-selected. 38 Although the high-precision velocity control enabled by Stark or Zeeman decelerators clearly provides great benefits, it is possible to determine information on the DCS correlated with the degree of rotational excitation in the collision partner in more conventional crossed-beam VMI experiments. 39,40 Significant new mechanistic insight can still be provided by these lower-resolution experiments, as demonstrated by Sun et al, who uncovered a new mechanism in CO + CO inelastic scattering, in which both CO molecules experienced high rotational excitation while undergoing forward scattering, which they dubbed forward-scattered symmetric excitation (FSSE).…”

Cold collisions of hot molecules

“…Using the crossed beam technique with a Stark decelerator, inelastic scattering resonances for nitric oxide (NO) with many targets have been successfully studied by van de Meerakker and co-workers with extraordinary control over the collision energy and collision energy spread. 22–25 Resonances in Penning ionization of metastable atoms and few molecules have also been demonstrated using the merged beam technique by the groups of Narevicius and Osterwalder. 26–29 In the merged beam technique, a paramagnetic species (typically a metastable rare gas atom) is guided by a magnetic quadrupole to merge with a target beam for Penning ionization studies.…”