Design and characterization of a recoil ion momentum spectrometer for investigating molecular fragmentation dynamics upon MeV energy ion impact ionization

TL;DR

This paper introduces a new recoil ion momentum spectrometer designed to study molecular fragmentation dynamics caused by MeV energy ion impact, featuring velocity imaging, high angular collection, and successful testing with N2 and CH2Cl2 molecules.

Contribution

The paper presents a novel spectrometer design with velocity imaging and multi-hit coincidence detection, enabling detailed 3D momentum measurements of molecular fragments.

Findings

High angular and velocity resolution achieved

Complete agreement with existing fragmentation data

Effective detection of ionic fragments with ~8 eV kinetic energy

Abstract

We present the development and performance of a newly built recoil ion momentum spectrometer to study the fragmentation dynamics of ionized molecules. The spectrometer is based on the two-stage Wiley-McLaren geometry and satisfies both time and velocity focusing conditions. An electrostatic lens has been introduced in the drift region to achieve velocity imaging and higher angular collection. The spectrometer is equipped with a 2D position-sensitive detector with multi-hit coincidence electronics. Ionic fragments with kinetic energy ~ 8 eV can be detected with 4{\pi} collection. The overall performance of the spectrometer has been tested by carrying out three-dimensional ion imaging measurements for diatomic (N$_2$) and polyatomic (CH$_2$Cl$_2$) molecules under the impact of 1 MeV proton. Three-dimensional momentum and kinetic energy release distributions were derived from the measured position and time-of-flight spectra. The observed features of the various fragmentation channels as well as the measured kinetic energy release distributions are in complete agreement with the available data.