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Analysis of velocity-mapped ion images from high-resolution crossed-beam scattering experiments: a tutorial review.

Zastrow AV, Onvlee J, Parker DH, van de Meerakker SY - EPJ Tech Instrum (2015)

Bottom Line: When velocity map imaging is used, the Stark decelerator allows the measurement of scattering images with unprecedented radial sharpness and angular resolution.Common image analysis techniques that are used throughout in crossed beam experiments can result in systematic errors, in particular in the determination of collision energy, and the allocation of scattering angles to observed peaks in the angular scattering distribution.PACS Codes: 34.50.-s; 37.10.Mn.

View Article: PubMed Central - PubMed

Affiliation: Radboud University, Institute for Molecules and Materials, Heijendaalseweg 135, Nijmegen, 6525 AJ Netherlands.

ABSTRACT

A Stark decelerator produces beams of molecules with high quantum state purity, and small spatial, temporal and velocity spreads. These tamed molecular beams are ideally suited for high-resolution crossed beam scattering experiments. When velocity map imaging is used, the Stark decelerator allows the measurement of scattering images with unprecedented radial sharpness and angular resolution. Differential cross sections must be extracted from these high-resolution images with extreme care, however. Common image analysis techniques that are used throughout in crossed beam experiments can result in systematic errors, in particular in the determination of collision energy, and the allocation of scattering angles to observed peaks in the angular scattering distribution. Using a high-resolution data set on inelastic collisions of velocity-controlled NO radicals with Ne atoms, we describe the challenges met by the high resolution, and present methods to mitigate or overcome them. PACS Codes: 34.50.-s; 37.10.Mn.

No MeSH data available.


Simulated scattering images for elastic NO-Ne collisions. The images illustrate the asymmetry in intensity and resolution due to the velocity spreads of the beams alone (a) and due to a combination of beam spreads and the flux-to-density effect (b). The simulation parameters pertain to the experimental conditions; in (a) the finite laser probe volume is neglected, whereas in (b) the probe volume is taken into account. In both simulations an isotropic DCS is assumed
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Fig6: Simulated scattering images for elastic NO-Ne collisions. The images illustrate the asymmetry in intensity and resolution due to the velocity spreads of the beams alone (a) and due to a combination of beam spreads and the flux-to-density effect (b). The simulation parameters pertain to the experimental conditions; in (a) the finite laser probe volume is neglected, whereas in (b) the probe volume is taken into account. In both simulations an isotropic DCS is assumed

Mentions: Let’s start with the inherent image resolution that results from the kinematics of the experiment. A collision between two particles can be represented by a Newton sphere, that is defined by its velocity radius and center-of-mass point. For such a Newton sphere, the scattering intensity is symmetric with respect to the relative velocity vector of the colliding particles. In a crossed beam experiment, however, collisions occur between particles from both beams, where each beam is characterized by its own angular and velocity spread. The effect of these spreads on the resolution of the image is illustrated in Fig. 6(a). This image shows a simulation for elastic collisions between NO and Ne, assuming an isotropic DCS and an infinitely large detection volume, i.e., all scattered molecules are detected with equal efficiency. The parameters of the simulation are chosen such to represent the conditions as present in our experiment (see section “Full simulations of the experiment”), i.e., the NO radicals have a much smaller angular and velocity spread compared to the Ne atom beam.Fig. 6


Analysis of velocity-mapped ion images from high-resolution crossed-beam scattering experiments: a tutorial review.

Zastrow AV, Onvlee J, Parker DH, van de Meerakker SY - EPJ Tech Instrum (2015)

Simulated scattering images for elastic NO-Ne collisions. The images illustrate the asymmetry in intensity and resolution due to the velocity spreads of the beams alone (a) and due to a combination of beam spreads and the flux-to-density effect (b). The simulation parameters pertain to the experimental conditions; in (a) the finite laser probe volume is neglected, whereas in (b) the probe volume is taken into account. In both simulations an isotropic DCS is assumed
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4551116&req=5

Fig6: Simulated scattering images for elastic NO-Ne collisions. The images illustrate the asymmetry in intensity and resolution due to the velocity spreads of the beams alone (a) and due to a combination of beam spreads and the flux-to-density effect (b). The simulation parameters pertain to the experimental conditions; in (a) the finite laser probe volume is neglected, whereas in (b) the probe volume is taken into account. In both simulations an isotropic DCS is assumed
Mentions: Let’s start with the inherent image resolution that results from the kinematics of the experiment. A collision between two particles can be represented by a Newton sphere, that is defined by its velocity radius and center-of-mass point. For such a Newton sphere, the scattering intensity is symmetric with respect to the relative velocity vector of the colliding particles. In a crossed beam experiment, however, collisions occur between particles from both beams, where each beam is characterized by its own angular and velocity spread. The effect of these spreads on the resolution of the image is illustrated in Fig. 6(a). This image shows a simulation for elastic collisions between NO and Ne, assuming an isotropic DCS and an infinitely large detection volume, i.e., all scattered molecules are detected with equal efficiency. The parameters of the simulation are chosen such to represent the conditions as present in our experiment (see section “Full simulations of the experiment”), i.e., the NO radicals have a much smaller angular and velocity spread compared to the Ne atom beam.Fig. 6

Bottom Line: When velocity map imaging is used, the Stark decelerator allows the measurement of scattering images with unprecedented radial sharpness and angular resolution.Common image analysis techniques that are used throughout in crossed beam experiments can result in systematic errors, in particular in the determination of collision energy, and the allocation of scattering angles to observed peaks in the angular scattering distribution.PACS Codes: 34.50.-s; 37.10.Mn.

View Article: PubMed Central - PubMed

Affiliation: Radboud University, Institute for Molecules and Materials, Heijendaalseweg 135, Nijmegen, 6525 AJ Netherlands.

ABSTRACT

A Stark decelerator produces beams of molecules with high quantum state purity, and small spatial, temporal and velocity spreads. These tamed molecular beams are ideally suited for high-resolution crossed beam scattering experiments. When velocity map imaging is used, the Stark decelerator allows the measurement of scattering images with unprecedented radial sharpness and angular resolution. Differential cross sections must be extracted from these high-resolution images with extreme care, however. Common image analysis techniques that are used throughout in crossed beam experiments can result in systematic errors, in particular in the determination of collision energy, and the allocation of scattering angles to observed peaks in the angular scattering distribution. Using a high-resolution data set on inelastic collisions of velocity-controlled NO radicals with Ne atoms, we describe the challenges met by the high resolution, and present methods to mitigate or overcome them. PACS Codes: 34.50.-s; 37.10.Mn.

No MeSH data available.