With a second OPG with tunable wavelengths in the UV and VIS installed in the lab, a host of new spectroscopic techniques can be explored, one of which is stimulated emission pumping. IR Hole Burning is a staple technique used in the de Vries lab that can uncover high resolution, tautomer specific, vibrational modes of a molecule, cluster, or complex in the gas phase. But it is limited by the wavelengths of light producible by our laser systems. To probe these unreachable regions, we will utilize a technique known as stimulated emission pumping modified to work with the action spectroscopy experiments we perform in the lab.

Stimulated emission pumping is a 3 photon process. Like hole burning, 2 photons at a fixed known resonant wavelength excite and ionize the sample molecule to be detected by the TOF mass spectrometer. Temporally between the excitation and ionization pulses, a third photon is scanned through a range of wavelengths low enough in energy to not allow for ionization with the photon. Unlike the usual resonant absorption techniques we use, this photon is scanned until a resonance between the current excited vibronic state and a lower energy excited vibronic state is found. This results in the excited electron undergoing stimulated emission, forcing the excited electron to a lower energy state previously not reachable. Additionally, this process is resonant, meaning that the likelihood of a successful emission is much more probable than other techniques like Raman that similarly probe low-lying vibrational states. If a successful resonant emission occurs, the excited population will decrease resulting in a drop of ionization signal and a spectra similar to hole burning. Stimulated Emission Pumping can thus be used to generate the ground state vibrational spectra of molecules.

Since this technique is new to the group, we will first demonstrate the proficiency of the technique using model systems that we have previously studied like the DNA bases and analogues. We then will apply the technique to larger complexes that would benefit from uncovering more complete vibrational spectra.