High-resolution vibrational spectroscopy is a theme that runs throughout our work. To achieve high spectral resolution, continuous wave infrared lasers are used in combination with a free jet vacuum apparatus that cools the sample molecules to a few degrees Kelvin. Cavity ringdown spectroscopy allows us to achieve very high sensitivity. Through collaborations with other institutions, we also use coherence-detected infrared-microwave double resonance spectroscopy (University of Virginia), infrared laser-assisted photofragment spectroscopy (Swiss Federal Institute, Lausanne), and slit-jet Fourier transform infrared spectroscopy (Pacific Northwest National Lab). These techniques are particularly effective in uncovering the couplings among the various molecular vibrations and with rotational motion.
Our work in this area has focused on the infrared spectroscopy of halocarbon compounds. Some halocarbons (CFCs) that are implicated in depletion of the stratospheric ozone layer have been banned. The replacement compounds (HFCs and HCFCs) that are now used in refrigeration and air conditioning still absorb in the infrared atmospheric window and, therefore, contribute to global warming. We are also interested in the spectroscopy of fuels used in combustion and of chemicals produced by combustion in the course of producing energy.
When a molecule is excited with a substantial amount of vibrational energy, the energy does not stay in the prepared vibration but redistributes to other degrees of freedom within the molecule. This phenomenon, termed IVR, is an essential ingredient in understanding the chemical reactivity of excited molecules. When IVR occurs, spectral splittings are observed, such as those illustrated below for nitromethane. We have found that IVR is faster in flexible molecules; therefore, we are studying molecules with large amplitude motions such as internal rotation.
Theoretical work in our group is undertaken in support of the experimental effort in the above areas. This work includes quantum mechanical models of IVR and ab initio molecular structure calculations.
- David S. Perry , Torsion-vibration coupling in methanol: Diabatic behavior in the CH overtone region, J. Phys. Chem. A 112, 215-223 (2008)
- Pavel Maksyutenko, Oleg V. Boyarkin, Thomas R. Rizzo and David S. Perry, Conformational dependence of intramolecular vibrational redistribution in methanol, J. Chem. Phys., 126, 044311 (2007) (6 pages)
- Trocia N Clasp and David S Perry, Torsion-vibration coupling in methanol: The adiabatic approximation and IVR scaling, J. Chem. Phys., 125, 104313 (2006). (9 pages)
- Michael J. Kulis, David S. Perry, Fletcher Miller, John Easton and Nancy Piltch, Fuel concentration measurements during flame spread in non-homogeneous gas mixtures, Fourth Jt. Meet. U.S. Sect. Combust. Inst.: West. States, Cent. States, East. States, B16/1-B16/6 (2005).
- David Rueda, Oleg V. Boyarkin, Thomas R. Rizzo, Andrei Chirokolava and David S. Perry, Vibrational overtone spectroscopy of jet-cooled methanol from 5,000 to 14,000 cm-1, J. Chem. Phys., 122, 044314 (2005). (8 pages)
- Shucheng Xu, Jeffrey J. Kay, and David S. Perry, Doppler-limited CW infrared cavity ringdown spectroscopy of the n1+n3 OH+CH stretch combination band of jet-cooled methanol, J. Mol. Spectrosc. 225, 162-173 (2004).
- Trocia N. Clasp, The theoretical study of torsion-vibrational dynamics in methanol and the improvement of CW-CRDS experimental apparatus, 2007.
- Michael J. Kulis, Concentration measurements during flame spread in terrestrial and microgravity environments, 2008.
- Sylvestre Twagirayezu, Vibrational relaxation pathways and torsional large amplitude motion studies in the CH-stretch region of CH3OH and CH3OD, 2011.
- Ram S. Bhatta, dynamics of coupled large amplitude motions from small nonrigid molecules to conjugated polymers, 2012,