Cold Chemistry/Cold Molecules is a branch of Physical Chemistry that deals with the behaviours of atoms and molecules (and its interaction - elastic, inelastic, reactive) at extremely low temperatures - close to absolute zero. Temperatures below 10 K and down to the miliKelvin regime is referred to as "cold" and temperatures below that as "ultracold". At these temperatures the de Broglie wavelength become comparable to the intermolecular separation - quantum effects start dominating the interaction between atoms and molecules, resulting in (experimental) observation of quantum phenomena such as resonance and tunnelling.
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. As a chemist this is the most salient feature of this research field as it enables us to get the first look at what exactly happens during the 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 the temperature, pressure and number densities are similar to that of that within the experimental apparatus, and 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 our laboratory we probe the quantum effects in the interaction between atoms and molecules experimentally by using a combination of techniques such as supersonic beam merging, velocity-map imaging, time-of-flight mass spectrometry, laser spectroscopy to achieve the said goal.