Multi-Particle Three-Dimensional Covariance Imaging: “Coincidence” Insights into the Many-Body Fragmentation of Strong-Field Ionized D₂O

Abstract

We demonstrate the applicability of covariance analysis to three-dimensional velocity-map imaging experiments using a fast time stamping detector. Studying the photofragmentation of strong-field doubly ionized D 2 O molecules, we show that combining high count rate measurements with covariance analysis yields the same level of information typically limited to the "gold standard" of true, low count rate coincidence experiments, when averaging over a large ensemble of photofragmentation events. This increases the effective data acquisition rate by approximately 2 orders of magnitude, enabling a new class of experimental studies. This is illustrated through an investigation into the dependence of three-body D 2 O 2+ dissociation on the intensity of the ionizing laser, revealing mechanistic insights into the nuclear dynamics driven during the laser pulse. The experimental methodology laid out, with its drastic reduction in acquisition time, is expected to be of great benefit to future photofragment imaging studies.

Multi-mass velocity map imaging study of the 805 nm strong field ionization of CF3I

“…To date, however, successful examples of three-fold covariance analysis generally require the collection of significantly more data (better statistics) than achieved in the present work and/or have been limited to relatively simple molecules with a modest number of dissociative pathways (e.g. the covariance between the D + , D + , O + fragments arising in the dissociation of D 2 O 3+ parent ions 59 ). Any such experiment on highly charged CF 3 I Z+ ions would surely benefit from pre-alignment of the parent molecules to simplify the data analysis and interpretation, as demonstrated in earlier ground-breaking CEI studies of pre-aligned 3,5-dibromo-3 0 ,5 0difluoro-4 0 -cyanobiphenyl molecules.…”

Cumulant mapping as the basis of multi-dimensional spectrometry

“…1. Moreover, the spectra of the (Z,Y, X, ...) variables could be more than 1-dimensional, for example, they could be sourced from a position-sensitive timing detector, which effectively resolves fragments in 3D momentum space 9 , and in principle would require mapping in 3n-dimensional space, unless the fragmentation kinematics can be used to reduce the dimen-J o u r n a l N a me , [ y e a r ] , [ v o l . ] ,…”

“…Cumulant mapping spectrometry can be combined with laserinduced fragmentation. On one hand, such combination allows us to elucidate the dynamics of molecular ionisation and fragmentation 9 , on the other hand, it makes it possible to tune the fragmentation to specific bonds in large biomolecules 24 .…”

Cumulant mapping as the basis of multi-dimensional spectrometry

“…1. Moreover, the spectra of the (Z, Y, X, ...) variables could be more than 1dimensional, for example, they could be sourced from a position-sensitive timing detector, which effectively resolves fragments in 3D momentum space [9], and in principle would require mapping in 3n-dimensional space, unless the fragmentation kinematics can be used to reduce the dimensionality.…”

“…Cumulant mapping spectrometry can be combined with laser-induced fragmentation. On one hand, such combination allows us to elucidate the dynamics of molecular ionization and fragmentation [9], on the other hand, it makes it possible to tune the fragmentation to specific bonds in large biomolecules [24].…”