The design and construction of a high-resolution velocity-map imaging apparatus for photoelectron spectroscopy studies of size-selected clusters

Abstract

A new velocity-map imaging apparatus equipped with a laser-vaporization supersonic cluster source and a time-of-flight mass spectrometer is described for high-resolution photoelectron spectroscopy studies of size-selected cluster anions. Vibrationally cold anion clusters are produced using a laser-vaporization supersonic cluster source, size-selected by a time-of-flight mass spectrometer, and then focused co-linearly into the interaction zone of the high-resolution velocity-map imaging (VMI) system. The multilens VMI system is optimized via systematic simulations and can reach a resolution of 1.2 cm(-1) (FWHM) for near threshold electrons while maintaining photoelectron kinetic energy resolutions (ΔKE/KE) of ~0.53% for higher energy electrons. The new VMI lens has superior focusing power over a large energy range, yielding highly circular images with distortions no larger than 1.0025 between the long and short radii. The detailed design, simulation, construction, testing, and performance of the high-resolution VMI apparatus are presented.

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

“…Several alternative VMI designs with excellent focusing capability for photoelectrons have been reported in the literature (55)(56)(57). The key changes made in these designs include adding a fourth electrode whose voltage is adjusted to optimize focus (55,57) and increasing the total length of the VMI stack (56).…”

“…The key changes made in these designs include adding a fourth electrode whose voltage is adjusted to optimize focus (55,57) and increasing the total length of the VMI stack (56). Increasing the length of the VMI lens along the electron flight axis can significantly improve its focusing ability, as the volume of the interaction region is smaller relative to the size of the lens.…”

Communication: Vibrationally resolved photoelectron spectroscopy of the tetracyanoquinodimethane (TCNQ) anion and accurate determination of the electron affinity of TCNQ

“…The experiment was done using our recently developed high-resolution photoelectron imaging apparatus, 20 which consists of an electrospray ionization (ESI) source, 21 a cryogenic ion trap, 22 a time-of-flight (TOF) mass spectrometer, and a high-resolution velocity-map imaging (VMI) analyzer. 23 Briefly, the TCNQ − anions were produced by electrospray of a 1 mM solution of TCNQ (Sigma-Aldrich) dissolved in acetonitrile and spiked with a small amount of NaI. Two radio-frequency (RF) quadrupole ion guides and one RF octopole ion guide directed the anions from the ESI source into a cryogenically cooled Paul trap operated at 4.5 K. The stored anions were cooled via collisions with 1 mTorr He/H 2 (4/1 in volume) buffer gas.…”

Communication: Observation of dipole-bound state and high-resolution photoelectron imaging of cold acetate anions

“…The anions were accumulated and cooled via collisions with a He/H 2 (4:1 volume ratio) buffer gas (∼1 mTorr) in the ion trap for 0.1 s before being pulsed out into the extraction zone of a time-of-flight mass spectrometer and selected by a mass gate. The CH 3 COO − anions were focused into a co-linear velocitymap imaging lens, 41 where anions were photodetached by a linearly polarized laser beam. Photoelectrons were projected onto a position-sensitive detector with a pair of 75-mm diameter micro-channel plates coupled to a phosphor screen and captured by a charge-coupled device camera.…”

“…Our high-resolution PE imaging apparatus 41 is equipped with an electrospray ionization (ESI) source, 42 a temperaturecontrolled cryogenic ion trap, [11][12][13] and a time-of-flight mass spectrometer. This apparatus is an improved version based on our original ESI-PES system that consisted of a roomtemperature ion trap and a magnetic-bottle PES analyzer.…”