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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.


Schematic representation of the experimental set-up. A pulsed beam of NO radicals is passed through a 2.6-meter long Stark decelerator, and is scattered with a pulsed beam of rare gas atoms at a 90 ° beam intersection angle. The inelastically scattered NO radicals are state-selectively ionized without excess recoil energy using two pulsed lasers. The ions are subsequently detected using a standard velocity map imaging arrangement
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Fig1: Schematic representation of the experimental set-up. A pulsed beam of NO radicals is passed through a 2.6-meter long Stark decelerator, and is scattered with a pulsed beam of rare gas atoms at a 90 ° beam intersection angle. The inelastically scattered NO radicals are state-selectively ionized without excess recoil energy using two pulsed lasers. The ions are subsequently detected using a standard velocity map imaging arrangement

Mentions: Measurements were performed in a crossed beam apparatus that is schematically shown in Fig. 1. The set-up, the Stark decelerator, and experimental procedures have been described in detail before [2–4]. Briefly, a molecular beam of NO radicals is formed by expanding a few percent NO in krypton through a Nijmegen Pulsed Valve [11]. After passage through a 3 mm diameter skimmer that is located about 100 mm from the nozzle orifice, the beam enters the 2.6-meter long Stark decelerator that consists of 317 pairs of high-voltage electrodes. The Stark decelerator is operated such that a packet of NO radicals emerges from the decelerator with a mean velocity of 370 m/s, a velocity spread of 2.4 m/s, and an angular spread of 0.1 ° (throughout this manuscript we refer to spreads as 1 σ of a Gaussian distribution). The Stark decelerator only transmits molecules that are in a low-field seeking quantum state, and approximately 99 % of the NO radicals that exit the decelerator reside in the upper Λ-doublet level of the X2Π1/2,v=0,j=1/2 rovibrational ground state. This state has f parity and is labeled hereafter as (1/2f); see Fig. 2 for a rotational energy level diagram of NO in its electronic and vibrational ground state.Fig. 1


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)

Schematic representation of the experimental set-up. A pulsed beam of NO radicals is passed through a 2.6-meter long Stark decelerator, and is scattered with a pulsed beam of rare gas atoms at a 90 ° beam intersection angle. The inelastically scattered NO radicals are state-selectively ionized without excess recoil energy using two pulsed lasers. The ions are subsequently detected using a standard velocity map imaging arrangement
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Schematic representation of the experimental set-up. A pulsed beam of NO radicals is passed through a 2.6-meter long Stark decelerator, and is scattered with a pulsed beam of rare gas atoms at a 90 ° beam intersection angle. The inelastically scattered NO radicals are state-selectively ionized without excess recoil energy using two pulsed lasers. The ions are subsequently detected using a standard velocity map imaging arrangement
Mentions: Measurements were performed in a crossed beam apparatus that is schematically shown in Fig. 1. The set-up, the Stark decelerator, and experimental procedures have been described in detail before [2–4]. Briefly, a molecular beam of NO radicals is formed by expanding a few percent NO in krypton through a Nijmegen Pulsed Valve [11]. After passage through a 3 mm diameter skimmer that is located about 100 mm from the nozzle orifice, the beam enters the 2.6-meter long Stark decelerator that consists of 317 pairs of high-voltage electrodes. The Stark decelerator is operated such that a packet of NO radicals emerges from the decelerator with a mean velocity of 370 m/s, a velocity spread of 2.4 m/s, and an angular spread of 0.1 ° (throughout this manuscript we refer to spreads as 1 σ of a Gaussian distribution). The Stark decelerator only transmits molecules that are in a low-field seeking quantum state, and approximately 99 % of the NO radicals that exit the decelerator reside in the upper Λ-doublet level of the X2Π1/2,v=0,j=1/2 rovibrational ground state. This state has f parity and is labeled hereafter as (1/2f); see Fig. 2 for a rotational energy level diagram of NO in its electronic and vibrational ground state.Fig. 1

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.