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Experimental
studies of the
multi-body
fragmentation
of polyatomic
molecules
using
coincidence
momentum
imaging
techniques
have become
more
attainable
with
advancements
in detector
and light
source
technologies.
The goal of
our research
group is to
apply these
techniques to
gain detailed
insight into
both concerted
and sequential
(also known as
simultaneous
and stepwise,
respectively)
molecular
dynamics, and
when possible,
follow their
time
evolution.
One common
approach for
relating the
momentum
images to the
stationary or
time-dependent
molecular
structure
relies on the
implementation
of Coulomb
explosion
imaging (CEI),
which inherently
assumes a
rapid
concerted
fragmentation.
This
assumption was
originally
fulfilled by
stripping fast
molecular ion
beams in
ultra-thin
foils [1].
However, in
photo-induced
molecular
processes the
validity of
this
assumption is
in question.
Clearly
sequential
fragmentation
is a process
that can
prevent the
proper
application of
CEI, and
therefore we
need to
separate
concerted and
sequential
fragmentation–a
goal that we
accomplish by
using native
frames
analysis [2].
The main
advantage of
the
native-frames
method is in
providing an
analysis and
interpretation
framework for
multi-body
fragmentation,
which is
typically
challenging
due to the
high
dimensionality
inherent in
such data. In
one example,
we study the
sequential
fragmentation
of D2O
molecules into
D++D++O+2e-
following
double
ionization by
a single
photon [3].
Namely, we
pinpoint the
precise
electronic
states
involved in
each
sequential
breakup step
and image the
internal
energy of the
OD+
intermediate
above the D++O(3P)
dissociation
limit. In
addition, we
show how the
angular
momentum of
the
intermediate
molecule
manifests as a
threshold
behavior in
the kinetic
energy release
of the second
breakup step.
We will also
discuss
experimental
progress
toward imaging
four-body
sequential
fragmentation
and toward
time-resolved
studies.
This work is
in
collaboration
with the
groups of
Daniel Rolles,
Artem Rudenko,
Thorsten
Weber, Bill
McCurdy,
Robert
Lucchese, Tom
Rescigno,
Daniel
Slaughter,
Joshua
Williams,
Allen Landers,
and Reinhard
Dörner.
References:
[1]
Z. Vager, R.
Naaman, and
E.P. Kanter,
Science 244,
426 (1989)
[2] J. Rajput,
T. Severt, et
al., Phys.
Rev. Lett. 120,
103001 (2018)
[3] T. Severt
et al.,
Nature
Communications
13,
5146 (2022)
*Supported
by the
Chemical
Sciences,
Geosciences,
and
Biosciences
Division,
Office of
Basic Energy
Sciences,
Office of
Science, U.S.
Department of
Energy under
Award No.
DE-FG02-86ER13491
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