Do single-bounce nuclear spin flips happen, and can they be measured?

Atoms, and consequently molecules, possess a fundamental property called nuclear spin. In simple terms, nuclear spin can be thought of as a microscopic magnet associated with each atom. Nuclear spins play a role in many very different fields, ranging from medical applications such as magnetic resonance imaging to efficient and safe storage of liquid hydrogen rocket fuel.

An important process in essentially all the applications which use nuclear spins, is the conversion of one spin state to another when the nuclear spins interact with each other and with their environment. Using the simple analogy to a magnet mentioned above, this can be considered as the microscopic magnet flipping its orientation.

In this project, we will attempt to look at a fundamental question in this field, which is whether the nuclear spin state of a molecule can change due to a single collision with a surface, and if it does, which types of surfaces and collision properties affect the probability of such a spin change. Conventional experimental techniques do not have the required sensitivity to follow such an event and the current level of theory cannot provide conclusive answers.

We will use a recently developed instrument which should be capable of sensing a spin change in a single collision. The instrument creates a beam of molecules in a well-defined nuclear spin state using various magnetic manipulations, aims them toward a solid surface, and then detects and analyses the spin state of the molecules emerging from the collision.

The results of this study are expected to contribute to our fundamental understanding of nuclear spin states, act as a benchmark for existing theoretical calculations, and eventually assist the development of more advanced theoretical models, which will be able to reliably model complex systems such as those encountered in the many scientific and industrial applications involving nuclear spins.