Trapping a molecule inside a liquid helium nanodrop allows clean measurements of the molecule’s vibrations.

The solvent in which a molecule is suspended can strongly influence the molecule’s motion. Now researchers have demonstrated that a molecule dissolved inside a superfluid helium nanodrop experiences very little effect from the solvent. The researchers measured, with femtosecond resolution, the intramolecular vibrations of an indium dimer (In₂) in a helium nanodrop. They say that their method could be used to study molecules relevant for light-harvesting technologies, such as solar cells, that have been difficult to observe because of solvent effects.