Simultaneous 3D coincidence imaging of cationic, anionic, and neutral photo-fragments

Abstract

We present the design and simulations of a 3D coincidence imaging spectrometer for fast beam photofragmentation experiments. Coincidence detection of cationic, neutral, and anionic fragments involves spectrometer aberrations that are successfully corrected by an analytical model combined with exact numerical simulations. The spectrometer performance is experimentally demonstrated by characterization of four different channels of intense 800 nm pulse interaction with F: F + F photodissociation, F + F dissociative photodetachment, F + F dissociative ionization, and F + F coulomb explosion. Improved measurement of F photodissociation with a 400 nm photon allows a better determination of the F anion dissociation energy, 1.256 ± 0.005 eV.

Time-resolving the ultrafast H2 roaming chemistry and H3+ formation using extreme-ultraviolet pulses

“…The nIR beam is mildly focused behind the spectrometer with a 610 mm lens,~203 mm behind the spectrometer, such that at the nIR beam is inside the EUV, as validated by using the spectrometer to image the parent ion birth positions. The cationic products are accelerated from the interaction volume towards a time and position sensitive detector, allowing 3D coincidence imaging of the ion recoil velocities [43][44][45] . Low count rate and center of mass momentum conservation are used to suppress random coincidence cation signal due to dissociative ionization of two different parent molecules.…”

Ultrafast F2− photodissociation by intense laser pulses: a time-resolved fragment imaging study

“…[ cationic, as well as neutral fragments resulting from interaction of ultrafast intense laser pulses with mass selected atomic, molecular and cluster anion systems. [11,13] 3D coincidence imaging of all atomic and molecular fragments allows disentangling of the competing mechanism for each molecular dissociation event at a time. The F2‾ anions are prepared in an Even-Lavie cold ion source, accelerated and mass selected before reaching a dedicated photofragment spectrometer.…”

“…Our previous investigations provide evidence for an efficient non-sequential mechanism, which is not based on the rescattering dynamics that dominates intense field interactions with neutral systems. [9][10][11][12][13] In a recent study of the relatively simple F2‾ system, double photodetachment and Coulomb explosion were shown to successfully compete with photodissociation on low lying dissociative states. [12] In this paper, we focus on the linear versus the non-linear effects observed in the ultrafast photodissociation of F2‾.…”

Double Photodetachment of F–·H2O: Experimental and Theoretical Studies of [F·H2O]+

“…Our fast beam fragment imaging spectrometer allows simultaneous detection of possible anionic, cationic, as well as neutral fragments resulting from interaction of ultrafast intense laser pulses with mass-selected anion systems . Three-dimensional coincidence imaging of laser–anion interaction products allows us to disentangle the different fragmentation channels. , Figure shows coincidence map analysis of correlated fragments of the F – ·H 2 O complex, allowing assignment of the observed dissociation events based on each fragment’s time-of-flight (TOF).…”

“…The kinetic energy released upon dissociation leads to recoil along the TOF axis, resulting in overlap of neighboring cation masses and making individual event assignment unfeasible. Nevertheless, as shown in Figure , the deconvolution of the contributions of different channels is possible by fitting the measured TOF distribution with simulated dissociative ionization distributions . Independent proton and neutral hydrogen products could not be detected in these experiments because of their low lab-frame momenta.…”