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Imaging Based on Absorption and Ion Detection Methods
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
While ion imaging began and very much thrived on unimolecular collision scenarios, studies of the dynamics of bimolecular reaction have become increasingly popular and are now routine in many research laboratories, a testimonial to which is the topical issue “Developments and Applications of Velocity Mapped Imaging Techniques” of The Journal of Chemical Physics (July 2017 issue), with an introductory perspective of the pioneers of the technique (Chandler et al. 2017). The application of ion imaging to bimolecular collisions requires combining crossed molecular-beam techniques and laser spectroscopic ionization with ion imaging. Laser radiation is employed to ionize (normally via a suitable REMPI scheme) a specific rotational–vibrational state of a nascent product formed in the crossed molecular-beam reaction. Imaging of the probe ions allows for the simultaneous measurement of the product angle and speed distributions, from which the state-resolved DCS can be determined (this will be discussed further in the following).
Combined crossed molecular beams and computational study on the N(2D) + HCCCN(X1Σ+) reaction and implications for extra-terrestrial environments
Published in Molecular Physics, 2022
Pengxiao Liang, Luca Mancini, Demian Marchione, Gianmarco Vanuzzo, Francesco Ferlin, Pedro Recio, Yuxin Tan, Giacomo Pannacci, Luigi Vaccaro, Marzio Rosi, Piergiorgio Casavecchia, Nadia Balucani
The experiments were carried out using a crossed molecular beam apparatus coupled with a quadrupole mass spectrometer and time-of-flight (TOF) analysis. The experimental approach has been described in detail elsewhere [44–46], and only a brief description is given here. Two supersonic beams were crossed at an intersection angle (γ) of 90°in the scattering chamber. During the experiment, the pressure was maintained at about 7×10−5 Pa to ensure single-collision conditions. Product angular and velocity distributions were measured by an electron impact ioniser followed by a quadrupole mass analyzer and a Daly ion detector contained in a triply differentially pumped ultrahigh vacuum (UHV) chamber which can be rotated in the collision plane around the intersection axis of the two beams.
Post extraction inversion slice imaging for 3D velocity map imaging experiments
Published in Molecular Physics, 2021
Felix Allum, Robert Mason, Michael Burt, Craig S. Slater, Eleanor Squires, Benjamin Winter, Mark Brouard
Measuring an entire three-dimensional velocity distribution, as opposed to a planar projection presents clear advantages in experimental geometries lacking an axis of cylindrical symmetry in the plane of the detector, for which the inverse Abel transform is not appropriate. Such experiments include crossed molecular beam scattering, and photofragment angular momentum polarisation experiments, employing non-colinear pump and pulse laser polarisations. Here, we demonstrate that three-dimensional velocity distributions, and thus photofragment anisotropy parameters can be reliably extracted from a set of PEISI imaging data directly, making no assumptions about the symmetry of the system, nor through the fitting of the data to any basis set. In terms of potential applications to studies of photofragment angular polarisation, these results suggest desired alignment parameters could be extracted from measurements in a single experimental geometry, circumventing the need to record data with multiple geometries of the polarisations of pump and probe pulses.
Charge transfer dynamics in Ar+ + CO
Published in Molecular Physics, 2021
T. Michaelsen, T. Gstir, B. Bastian, E. Carrascosa, A. Ayasli, J. Meyer, R. Wester
We have measured the differential cross sections for the charge-transfer reaction Ar+(P) + CO in our crossed molecular beam setup using the VMI technique. In Figure 2(a,e) the velocity images of the product CO+ ion are shown at the two different collision energies (0.55 and 0.74 eV). The white and black solid rings represent the kinematic cutoff (maximum available kinetic energy) and the dashed inner rings the expected velocity of the CO+ product ions in the vibrational levels = 6i,7ii. If the process resonantly couples to the closest reachable product state, the expected velocity distribution should peak around these dashed inner rings. Furthermore, the red ring in the velocity image for 0.74 eV collision energy corresponds to the energy needed to access the first electronically excited state A, which is not accessible at the lower collision energy (see also Figure 1).