17 research outputs found
Quantum state resolved molecular dipolar collisions over four decades of energy
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 NO and ND 3 molecules at
energies between 0.1 and 580 cm-1 , with full quantum state resolution. At
energies below the 100 cm-1 well depth of the interaction potential, we
observed backward glories originating from peculiar U-turn trajectories. At
energies below 0.2 cm-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-ND3 potential energy surface revealed the
crucial role of near-degenerate rotational levels with opposite parity in
low-energy dipolar collisions
Imaging the onset of the resonance regime in low-energy NO-He collisions
At low energies, the quantum wave-like nature of molecular interactions
result in unique scattering behavior, ranging from the universal Wigner laws
near zero Kelvin to the occurrence of scattering resonances at higher energies.
It has proven challenging to experimentally probe the individual waves
underlying these phenomena. We report measurements of state-to-state integral
and differential cross sections for inelastic NO-He collisions in the 0.2 - 8.5
cm range with 0.02 cm resolution. We study the onset of the
resonance regime by probing the lowest-lying resonance dominated by s and p
waves only. The highly structured differential cross sections directly reflect
the increasing number of contributing waves as the energy is increased. A new
NO-He potential calculated at the CCSDT(Q) level was required to reproduce our
measurements.Comment: 14 pages, 4 figure
Observation of correlated excitations in bimolecular collisions
Whereas collisions between atoms and molecules are largely understood,
collisions between two molecules have proven much harder to study. In both
experiment and theory, our ability to determine quantum state-resolved
bimolecular cross sections lags behind their atom-molecule counterparts by
decades. For many bimolecular systems, even rules of thumb -- much less
intuitive understanding -- of scattering cross sections are lacking. Here, we
report the measurement of state-to-state differential cross sections on the
collision of state-selected and velocity-controlled nitric oxide (NO) radicals
and oxygen (O2) molecules. Using velocity map imaging of the scattered NO
radicals, the full product-pair correlations of rotational excitation that
occurs in both collision partners from individual encounters are revealed. The
correlated cross sections show surprisingly good agreement with quantum
scattering calculations using ab initio NO-O2 potential energy surfaces. The
observations show that the well-known energy-gap law that governs atom-molecule
collisions does not generally apply to bimolecular excitation processes, and
reveal a propensity rule for the vector correlation of product angular momenta.Comment: Received: 06 September 2017 Accepted: 20 December 2017 Published
online: 19 February 2018, Nature Chemistry 201
Highlights from the Faraday Discussion 296: quantum effects in small molecular systems, 10-12 September 2018, Edinburgh, United Kingdom
Contains fulltext :
199083.pdf (publisher's version ) (Closed access
Assessing neutral transport mechanisms in aspect ratio dependent etching by means of experiments and multiscale plasma modeling
Diabatic states, nonadiabatic coupling, and the counterpoise procedure for weakly interacting open-shell molecules
Contains fulltext :
190040.pdf (publisher's version ) (Open Access)15 p
High-resolution imaging of molecular collisions using a Zeeman decelerator
Contains fulltext :
218188.pdf (publisher's version ) (Open Access
Correlations in rotational energy transfer for NO-D-2 inelastic collisions
Contains fulltext :
224904.pdf (publisher's version ) (Open Access