Experimental physical chemistry: photochemistry; laser spectroscopy; reaction dynamics of vibrationally excited molecules
Massachusetts Institute of Technology
Case Western Reserve University
Awards and Academic Honors
Postdoctoral Fellow, University of Wisconsin, Madison
Postdoctoral Fellow, National Oceanic and Atmospheric Administration
Research in our laboratory is directed towards investigating state-resolved reaction dynamics of gas phase molecules. We use laser excitation to prepare reagent molecules in specific quantum states and follow their subsequent dynamics using frequency and time resolved spectroscopy. The selectivity achieved in both the reactant state preparation and product detection steps allow us to nullify the influence of thermal averaging and obtain detailed state-to-state data that are crucial for testing prevailing theories about the dynamics. A particularly exciting research area of current interest involves examining the influence of molecular vibrations on various chemical processes such as photodissociation, unimolecular reactions, and bimolecular reactions. In these studies we use highly state selective excitation schemes such as vibrational overtone-overtone double resonance to energize the reagent molecule and then probe the consequences of the state preparation on the ensuing dynamics by detecting the reaction products using laser induced fluorescence in conjunction with sub-Doppler spectroscopy. Photodissociation experiments on vibrationally excited molecules, for example, allow us to access regions of the electronic excited state surface that are normally inaccessible from the ground state, and hence have the potential for revealing novel photochemistry that is likely to be otherwise forbidden. In the case of unimolecular and bimolecular reactions, we use vibrational excitation not only to overcome the energetic threshold for reaction, but also to explore mode selectivity; that is, how vibrations having similar energy but corresponding to different nuclear motion affect reactivity. In favorable cases, vibrational mode selectivity can even be used to control the course of a reaction. In addition to dynamics, basic questions regarding the spectroscopy of vibrationally excited molecules are also of interest and analysis of "action" spectra, generated by monitoring the yield of a specific reaction product while scanning the frequency of the vibrational excitation laser, is used to glean information about the intramolecular interactions that control the flow of energy within the energized molecule. We are particularly interested in applying our experimental methods to transient species and molecular systems relevant to atmospheric and combustion chemistry.
Primary Research Area
Atmospheric and Environmental
Over the current years, I have acted as research advisor and mentor for several students and scholars from underrepresented groups in order to kindle their interest in science.
- OH-stretch vibrational spectroscopy of hydroxymethyl hydroperoxide, J. L. Fry, J. Matthews, J. R. Lane, C.M. Roehl, A. Sinha, H. G. Kjaergaard, and P. O. Wennberg; J. Phys. Chem. A , 110 , 7072 (2006).
- State-resolved unimolecular dissociation of Cis-Cis HOONO: Product state distribution and action spectrum in the 2vOH band region, J. Matthews and A. Sinha; J. Chem. Phys., 122 , 104313 (2005).
- The importance of weak absorption features in promoting tropospheric radical production, J. Matthews, A. Sinha, and J. S. Francisco; Proc. Natl. Acad. Sci. USA 102 , 7449 (2005).
- The OH stretching and OOH bending overtone spectrum of HOONO, D. P. Schofield, H. G. Kjaergaard, J. Matthews, and A. Sinha; J. Chem. Phys., 123 , 134318 (2005).
- Unimolecular dissociation and thermochemistry of CH3OOH, J. Matthews, A. Sinha, and J. S. Francisco; J. Chem. Phys., 122 , 22101 (2005).
- High Level ab initio Study of the Structure and Vibrational Spectra of HO2NO2, With J. Matthews and J. S. Francisco. J. Chem. Phys. 121, 5720 (2004).
- Photodissociation of Vibrationally Excited Pernitric Acid: HO2NO2(2v1) + 390 nm, With J. Matthews and R. Sharma.. J. Phys. Chem. A. 108, 8134 (2004).
- Relative Vibrational Overtone Intensity of cis-cis and trans-perp Peroxynitrous Acid(HOONO), With J. Matthews and J. S. Francisco. J. Chem. Phys. 120, 10543 (2004).