Photoelectron–multiple-photofragment coincidence spectrometer

Abstract

A new photoelectron-photofragment-coincidence spectrometer is described. Using a multiparticle time-and position-sensitive detector, this apparatus allows the study of dissociation processes of negative ions yielding three photofragments in coincidence with a photoelectron. The photoelectron spectrometer uses two detectors and works in time of flight mode, detecting 10% of the photoelectrons with an energy resolution of 5% at 1.3 eV as shown in studies of the photodetachment of O 2 Ϫ . A third detector is used for collection of multiple photofragments ͑up to 8͒ in coincidence. This multiparticle detector uses a crossed-delay-line anode and fast timing signals to encode the time-and position-of-arrival of multiple photofragments. The detector was demonstrated to record all three particles produced in a single three-body dissociation event, yielding an energy resolution of Ϸ15% ⌬E/E at 0.7 eV in experiments on the three-body dissociative photodetachment of O 6Ϫ .

Femtosecond Time-Resolved Photoelectron Spectroscopy

“…Very successful methods for full time-and position-sensitive detection are based upon interpolation (rather than pixellation) using either charge-division (such as "wedge-and-strip") 109,110 or crossed delay-line anode timing MCP detectors. 111,112 In the former case, the avalanche charge cloud is divided among three conductorssa wedge, a strip, and a zigzag. The (x,y) positions are obtained from the ratios of the wedge and strip charges to the zigzag (total) charge.…”

Dissociative Recombination Chemistry and Plasma Dynamics

“…Using the fast 6-16 keV beams available on this apparatus, however, non-resonant charge-exchange processes can produce species nearly at the ionization potential of the neutral target for a small molecular cation like H 3 + . Our efforts complement and extend earlier studies of DCE 3,4,5,6,7,8 through the use of vibrationally cold cations produced in a supersonic expansion and a state-of-the-art multiparticle detector, 9 permitting studies of two-and three-body dissociative charge exchange processes. In these experiments, a pulsed, fast (6 -16 keV) mass-selected cation beam was passed through a 1-mm long charge-exchange cell with a pressure of ≈10 -4 torr Cs.…”

Photodissociation Dynamics of the Thiophenoxy Radical at 248, 193, and 157 nm

“…37,40,41 The detector comprises a Z-stack of three 75 mm diameter MCPs with a 40:1 aspect ratio mounted to a delay line anode consisting of three layers of delay lines. When an incident particle strikes the front MCP, an electron cascade is produced, and the resulting charge cloud that emerges from the MCP stack is collected by the three-layered anode.…”