# A Coincidence Velocity Map Imaging Spectrometer for Ions and High-Energy Electrons to Study Inner-Shell Photoionization of Gas-Phase Molecules

## TL;DR

This paper introduces a specialized coincidence velocity map imaging spectrometer designed for studying inner-shell photoionization in gas-phase molecules, enabling detailed electron-ion and ion-ion correlation measurements with high energy resolution.

## Contribution

The paper presents a novel double-sided spectrometer setup optimized for coincidence detection of electrons and ions in inner-shell photoionization studies, demonstrating its capabilities with multiple molecular examples.

## Key findings

- Successful measurement of valence photoelectron and ion spectra of neon and nitrogen.
- Detailed channel-resolved photoelectron and Auger spectra for chlorine 2p ionization.
- Observation of fragment-ion momentum correlations in dichloroethene.

## Abstract

We report on the design and performance of a double-sided coincidence velocity map imaging spectrometer optimized for electron-ion and ion-ion coincidence experiments studying inner-shell photoionization of gas-phase molecules with soft X-ray synchrotron radiation. The apparatus employs two microchannel plate detectors equipped with delay-line anodes for coincident, time- and position-resolved detection of photo- and Auger electrons with kinetic energies up to 300\,eV on one side of the spectrometer and photoions up to 25\,eV per unit charge on the opposite side. We demonstrate its capabilities by measuring valence photoelectron and ion spectra of neon and nitrogen, and by studying channel-resolved photoelectron and Auger spectra along with fragment-ion momentum correlations for chlorine $2p$ inner-shell ionization of \textit{cis}- and \textit{trans}-1,2-dichloroethene.