Molecular collisions coming into focus

Abstract

The Stark deceleration method exploits the concepts of charged particle accelerator physics to produce beams of neutral polar molecules with an almost perfect quantum state purity, a tunable velocity and a narrow velocity distribution. These monochromatic molecular beams offer interesting perspectives for precise studies of molecular scattering processes, in particular when used in conjunction with state-of-the-art laser-based detection techniques such as velocity map imaging. Here, we describe crossed beam scattering experiments in which the Stark deceleration method is combined with the velocity map imaging technique. The narrow velocity spread of Stark-decelerated molecular beams results in scattering images with unprecedented velocity and angular resolution. We demonstrate this by resolving quantum diffraction oscillations in state-to-state inelastic differential scattering cross sections for collisions between NO radicals and rare gas atoms. We describe the future prospects of this "best-of-two-worlds" combination, ranging from scattering studies at low collision energies to bimolecular scattering using two decelerators, and discuss the challenges that lie ahead to achieve these goals.

Resonances in rotationally inelastic scattering of NH3 and ND3 with H2

“…70 The NH 3 molecule is particularly amenable to this combination of techniques, although the implementation of a recoilfree resonance-enhanced multi-photon ionization (REMPI) scheme can constitute a formidable challenge. 71 Experiments of this type are currently underway.…”

A new perspective: imaging the stereochemistry of molecular collisions

“…[79][80][81][82][83][84][85][86][87][88][89][90]). [79][80][81][82][83][84][85][86][87][88][89][90]).…”

High-Resolution Imaging of Velocity-Controlled Molecular Collisions Using Counterpropagating Beams

“…Clearly, these tamed molecular beams are ideally suited for precise molecular scattering experiments, in particular when combined with state-of-the art detection techniques such as VMI. Recently, we have reported the first crossed beam experiment in which a Stark decelerator was combined with VMI, indeed resulting in scattering images with much higher resolution [9,10].…”

“…The rare-gas atom beam is well collimated by placing a 1 mm wide slit between the 2 mm diameter skimmer and the interaction region. Scattered molecules are detected state selectively using a two-color laser ionization scheme and a standard VMI geometry [10,11]. The two laser beams are directed parallel to the detector plane and cross each other at right angles.…”

“…We use a crossed beam scattering apparatus in which a packet of NO (X 2 Π 1=2 ; j ¼ 1=2; f) radicals with a mean velocity of 350 m=s, a velocity spread of 2.1 m=s (1σ), and an angular spread of 0.1°(1σ) is produced by passing a beam of NO through a 2.6 m long Stark decelerator [10]. The packet of NO collides with a beam of Ne or Ar atoms at a beam intersection angle of 180°, resulting in a relatively high collision energy of 720 and 725 cm −1 for NO-Ne and NO-Ar, respectively.…”