Precision Spectroscopy with Single Polyatomic Molecules

We learn a great deal about the structure and quantum mechanical nature of molecules by studying how they absorb and emit light (spectroscopy). Almost all spectroscopy is done on samples containing many molecules. These large samples give large signals, but they come with a disadvantage - everything that is measured is actually an average value of the sample. For example, some molecules are moving fast, some are moving slowly, some are spinning, and so on. This variety limits the precision with which the molecules can be measured. In this work, the research team of undergraduate and graduate students and the principal investigator will use new, very sensitive techniques which can measure single molecules. The team will measure these single molecules very precisely - in fact, these measurements will be the most precise measurements ever made of molecules that are composed of more than two atoms. This precision will, in the future, allow scientists to use such molecules to search for new physics beyond that envisioned in our current theories. This research provides challenging, hands-on research projects for graduate and undergraduate students at the University of California, Santa Barbara. Action spectroscopy is a versatile technique capable of measuring the vibrational spectra of molecular ions. A new, powerful version of action spectroscopy, leak out spectroscopy, has recently been demonstrated on ensembles of molecules at temperatures of ~10 K. This method has yielded Doppler-limited vibrational spectra with resolution of about 100 MHz. The research team at the University of California, Santa Barbara will extend this technique, first into the single molecule regime at millikelvin temperatures, and then to the Lamb-Dicke regime, which exhibits no first order Doppler shift. This will give a resolution in the kHz regime, and will for the first time enable high-precision spectroscopy of a broad range of polyatomic molecular ions, including chiral molecular ions. The technique has applications in searches for new physics and nano-analytic chemistry. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.