Towards Vibrational Spectroscopy of Single Polyatomic Molecules

Molecular ions are of fundamental importance to fields from biochemistry to atmospheric chemistry. High resolution spectroscopy is challenging, however, as large number densities are difficult to achieve in the gas phase. Action spectroscopy methods enable high resolution structural studies otherwise inaccessible with absorption methods, but most all commonly reported action techniques destroy the molecules being studied. We are pursuing a novel action technique in which molecular ions are co-trapped with laser-cooled atomic ions and complexed with weakly bound, neutral "messenger" atoms. Messengers can be selectively removed by optically exciting vibrational transitions, and co-trapped atoms can be used as a probe to monitor this messenger ejection process, thus indirectly recording the vibrational spectrum of the trapped molecule. The instrument which we are building to perform these measurements will open up new pathways for non-destructive, high-resolution spectroscopy and structural analysis of molecular ions.