Speaker: Dr. Nabanita Deb
Indian Association for the Cultivation of Science,
Kolkata
Title: "Cold Chemistry: Probing quantum effects in atom-
molecule interactions at cold conditions".
Day and Date: Tuesday, August 22, 2023
Time: 11.30 am.
Venue: Seminar room, room no. 350, Chemistry Department
(second floor, Annex)
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Hosted by Prof. G. Naresh Patwari
Abstract Cold chemistry is the investigation of interactions of atoms and molecules at near-absolute-zero
temperatures, few-Kelvin to milli-Kelvin range. Cold conditions enable the study of chemical reactions with
full control over the reaction parameters. Colliding particles at these temperatures reveals quantum nature of
interaction between any atoms or molecules; quantum effects such as resonances become observable and lead
to sharp increase in collision cross section. Such unambiguous identification of resonances enables subtle
features on the underlying potential energy surfaces to be probed, enabling us to get the first look at what
exactly happens during a chemical reaction. Cold chemistry is also important for the understanding the rich
gas phase chemistry occurring at the interstellar medium and the upper atmosphere, where reactions are
expected to proceed through quantum mechanisms, unlike at room temperatures. Therefore, such experimental
measurements enable the accuracy of high-level theoretical calculations to be assessed and the validity of such
models of chemical reactivity to be tested. In the talk, I will show the results of an experiment, where a merged
beam method is used in combination with velocity map imaging technique to probe the dynamics of He
* – D2
collisions in the range 1.0 to 50.0 K experimentally. In our studies, we distinguish between two mechanisms
of formation of resonances by comparing the elastic and Penning ionization cross sections (this work has been
recently published in Nat. Chem., 13, 94, 2021). In this work we show two different resonances – shape and
orbiting in the interaction of He
*
and D2. Our results show resonances at 2.0, 4.0 and 8.0 K in the elastic
scattering cross section whereas only the 2.0 K resonance is visible in the Penning ionization spectra (fig. 1).
Shape resonances appear as sharp peaks in both processes whereas orbiting resonances only appear in the
elastic cross section since the probability of finding particles at short separation, where ionization takes place,
is small. In this work, we report the first experimental identification of these two mechanisms. I will also
discuss my future research interest.