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Title: Velocity map photoelectron-photoion coincidence imaging on a single detector

Abstract

Here we report on a new simplified setup for velocity map photoelectron-photoion coincidence imaging using only a single particle detector. We show that both photoelectrons and photoions can be extracted toward the same micro-channel-plate delay line detector by fast switching of the high voltages on the ion optics. This single detector setup retains essentially all the features of a standard two-detector coincidence imaging setup, viz., the high spatial resolution for electron and ion imaging, while only slightly decreasing the ion time-of-flight mass resolution. The new setup paves the way to a significant cost reduction in building a coincidence imaging setup for experiments aiming to obtain the complete correlated three-dimensional momentum distribution of electrons and ions.

Authors:
; ;  [1]
  1. LaserLaB Amsterdam, VU University Amsterdam, de Boelelaan 1083, 1081 HV Amsterdam (Netherlands)
Publication Date:
OSTI Identifier:
22093724
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 83; Journal Issue: 9; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ELECTRON DETECTION; ELECTRONS; IONS; MASS RESOLUTION; MASS SPECTROSCOPY; MICROCHANNEL ELECTRON MULTIPLIERS; PARTICLE BEAMS; PHOTOEMISSION; POSITION SENSITIVE DETECTORS; SPATIAL RESOLUTION; THREE-DIMENSIONAL CALCULATIONS; TIME-OF-FLIGHT METHOD; VELOCITY

Citation Formats

Lehmann, C. Stefan, Ram, N. Bhargava, and Janssen, Maurice H. M. Velocity map photoelectron-photoion coincidence imaging on a single detector. United States: N. p., 2012. Web. doi:10.1063/1.4749843.
Lehmann, C. Stefan, Ram, N. Bhargava, & Janssen, Maurice H. M. Velocity map photoelectron-photoion coincidence imaging on a single detector. United States. doi:10.1063/1.4749843.
Lehmann, C. Stefan, Ram, N. Bhargava, and Janssen, Maurice H. M. 2012. "Velocity map photoelectron-photoion coincidence imaging on a single detector". United States. doi:10.1063/1.4749843.
@article{osti_22093724,
title = {Velocity map photoelectron-photoion coincidence imaging on a single detector},
author = {Lehmann, C. Stefan and Ram, N. Bhargava and Janssen, Maurice H. M.},
abstractNote = {Here we report on a new simplified setup for velocity map photoelectron-photoion coincidence imaging using only a single particle detector. We show that both photoelectrons and photoions can be extracted toward the same micro-channel-plate delay line detector by fast switching of the high voltages on the ion optics. This single detector setup retains essentially all the features of a standard two-detector coincidence imaging setup, viz., the high spatial resolution for electron and ion imaging, while only slightly decreasing the ion time-of-flight mass resolution. The new setup paves the way to a significant cost reduction in building a coincidence imaging setup for experiments aiming to obtain the complete correlated three-dimensional momentum distribution of electrons and ions.},
doi = {10.1063/1.4749843},
journal = {Review of Scientific Instruments},
number = 9,
volume = 83,
place = {United States},
year = 2012,
month = 9
}
  • An imaging photoelectron photoion coincidence spectrometer at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source is presented and a few initial measurements are reported. Monochromatic synchrotron VUV radiation ionizes the cooled or thermal gas-phase sample. Photoelectrons are velocity focused, with better than 1 meV resolution for threshold electrons, and also act as start signal for the ion time-of-flight analysis. The ions are accelerated in a relatively low, 40-80 V cm{sup -1} field, which enables the direct measurement of rate constants in the 10{sup 3}-10{sup 7} s{sup -1} range. All electron and ion events are recorded in a triggerlessmore » multiple-start/multiple-stop setup, which makes it possible to carry out coincidence experiments at >100 kHz event frequencies. As examples, the threshold photoelectron spectrum of the argon dimer and the breakdown diagrams for hydrogen atom loss in room temperature methane and the chlorine atom loss in cold chlorobenzene are shown and discussed.« less
  • A novel threshold photoelectron-photoion coincidence (TPEPICO) imaging spectrometer at the U14-A beamline of the Hefei National Synchrotron Radiation Laboratory is presented. A set of open electron and ion lenses are utilized to map velocity imaging of photoelectrons and photoions simultaneously, in which a repelling electric field using an extra lens is applied to magnify images of photoelectrons instead of traditional accelerating electric field in order to suppress the contribution of energetic electrons in the threshold photoelectron spectroscopy (TPES) and the mass-selected TPEPICO spectroscopy. The typical energy resolution of TPES is measured to be 9 meV (full width at half maximum),more » as shown on the {sup 2}P{sub 1/2} ionization of argon. The measured mass resolving power for the present TPEPICO imaging spectrometer is above 900 of M/{Delta}M. Subsequently as a benchmark, oxygen molecule is photoionized by monochromatic synchrotron radiation at 20.298 eV and dissociates to an oxygen atomic ion and a neutral oxygen atom, and the translation energy distribution of oxygen atomic ion is measured by the time-sliced imaging based on mass-selected TPEPICO experiment. The kinetic energy resolution of the present ion velocity imaging is better than 3% of {Delta}E/E.« less
  • Dissociative photoionization of methyl bromide (CH{sub 3}Br) in an excitation energy range of 10.45–16.90 eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X{sup 2}E of CH{sub 3}Br{sup +} is stable, and both A{sup 2}A{sub 1} and B{sup 2}E ionic excited states are fully dissociative to produce the unique fragment ion of CH{sub 3}{sup +}. From TPEPICO 3D time-sliced velocity images of CH{sub 3}{sup +} dissociated from specific state-selected CH{sub 3}Br{sup +} ion, kinetic energy release distribution (KERD) and angular distribution of CH{sub 3}{sup +} fragment ionmore » are directly obtained. Both spin-orbit states of Br({sup 2}P) atom can be clearly observed in fast dissociation of CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion along C–Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH{sub 3}Br{sup +}(B{sup 2}E) ion. With the aid of the re-calculated potential energy curves of CH{sub 3}Br{sup +} including spin-orbit coupling, dissociation mechanisms of CH{sub 3}Br{sup +} ion in A{sup 2}A{sub 1} and B{sup 2}E states along C–Br rupture are revealed. For CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion, the CH{sub 3}{sup +} + Br({sup 2}P{sub 1/2}) channel is occurred via an adiabatic dissociation by vibration, while the Br({sup 2}P{sub 3/2}) formation is through vibronic coupling to the high vibrational level of X{sup 2}E state followed by rapid dissociation. C–Br bond breaking of CH{sub 3}Br{sup +}(B{sup 2}E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.« less
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  • We present the first results using a new technique that combines femtosecond pump{endash}probe methods with energy- and angle-resolved photoelectron{endash}photoion coincidence imaging. The dominant dissociative multiphoton ionization (DMI) pathway for NO{sub 2} at 375.3 nm is identified as three-photon excitation to a repulsive potential surface correlating to NO(Cthinsp{sup 2}{Pi})+O({sup 3}P) followed by one-photon ionization to NO{sup +}(Xthinsp{sup 1}{Sigma}{sup +}). Dissociation along this surface is followed on a femtosecond timescale. {copyright} {ital 1999 American Institute of Physics.}