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IMM colloquium "Taming Molecular Collisions" (Lecture)

Tuesday 24 April 2018Add to my calendar
from 15:45
prof. Bas van de Meerakker (Spectroscopy of Cold Molecules)

The study of molecular collisions with the highest possible detail has been an important research theme in physical chemistry for decades. Over the last years we have developed methods to get improved control over molecules in a molecular beam. With the Stark decelerator, a part of a molecular beam can be selected to produce bunches of molecules with a computer-controlled velocity and with longitudinal temperatures as low as a few mK. The molecular packets that emerge from the decelerator have small spatial and angular spreads, and have almost perfect quantum state purity. These tamed molecular beams are excellent starting points for high-resolution crossed beam scattering experiments.

I will discuss our most recent results on the combination of Stark deceleration and velocity map imaging. The narrow velocity spread of Stark-decelerated beams results in scattering images with an unprecedented sharpness and angular resolution. This has facilitated the observation of several scattering phenoma that reveal the quantum mechanical nature of the scattering process. Many of these phenomena have been theoretically predicted decades ago, but had remained elusive experimentally due to insufficient control over the scattering partners. These include diffraction oscillations in state-to-state differential cross sections, scattering resonances at collision energies near zero Kelvin and pair correlations for bi-molecular collisions.
Velocity mapped ion image for inelastic NO-Ar collisions, featuring a rich diffraction oscillation pattern. Adapted from Ref. [4].

[1] J.J. Gilijamse, S. Hoekstra, S.Y.T. van de Meerakker, G.C. Groenenboom, G. Meijer, Near-threshold inelastic collisions using molecular beams with a tunable velocity, Science 313, 1617 (2006)
[2] M. Kirste, X. Wang, H.C. Schewe, G. Meijer, K. Liu, A. van der Avoird, L.M.C. Janssen, K.B. Gubbels, G.C. Groenenboom, S.Y.T. van de Meerakker,      Quantum-state resolved bimolecular collisions of velocity-controlled OH with NO radicals, Science 338, 1060 (2012)
[3] A. von Zastrow, J. Onvlee, S.N. Vogels, G.C. Groenenboom, A. van der Avoird, S.Y.T. van de Meerakker, State-resolved diffraction oscillations imaged for inelastic collisions of NO radicals with He, Ne and Ar, Nature Chemistry 6, 216 (2014).
[4] S.N. Vogels, J. Onvlee, A. von Zastrow, G.C. Groenenboom, A. van der Avoird, S.Y.T. van de Meerakker,  High-resolution imaging of velocity-controlled molecular collisions using counter-propagating beams,Phys. Rev. Lett. 113, 263202 (2014).
[5] J. Onvlee et al., Imaging quantum stereodynamics through Fraunhofer scattering of NO radicals with rare-gas atoms, Nature Chemistry 9, 226 (2017).
[6] S. Chefdeville, Y. Kalugina, S.Y.T. van de Meerakker, C. Naulin, F. Lique, M. Costes, Observation of partial wave resonances in low-energy O2-H2 inelastic collisions, Science 341, 1094 (2013).
[7] S.N. Vogels, J. Onvlee, S. Chefdeville, A. van der Avoird, G.C. Groenenboom, S.Y.T. van de Meerakker, Imaging resonances in low-energy NO-He inelastic collisions, Science 350, 787 (2015).

prof. Arno Kentgens