Joseph L. Knee, Ph.D.

    Our group's research effort is directed toward understanding fundamental dynamic processes which occur in energized molecular systems. In particular, we use techniques of picosecond laser spectroscopy to measure the rates of such processes as intramolecular vibrational energy redistribution, electronic state non-radiative energy transfer and unimolecular dissociation. Picosecond laser pulses are used to excite molecules to specific energy states which then evolve under the influence of the above-mentioned dynamic processes. The time evolution of the initially-prepared state can be monitored by a variety of techniques (with resolution to approximately 10 picoseconds) and thus the rates of the dynamic processes can be inferred. The emphasis is on isolated molecules where one is measuring solely intramolecular effects.

    One area that we will be studying, which is of particular interest to chemists, is unimolecular dissociation reactions. In this case the energy deposited in the molecule by laser excitation is sufficient to break a chemical bond. The details of how the energy is transferred to the reaction coordinate is a question we are studying. Knowledge gained from these "model" systems can be applied to a variety of chemical systems where molecules become energized thermally or chemically, but are still subject to the same energy redistribution processes.

    The use and development of new techniques for measuring these ultrafast phenomena is a major part of our effort. Specific areas of development include novel fluorescence measurements, pump probe photoiionization techniques and the application of photoelectron spectroscopy to the measurement of dynamics of molecular states. In particular we have developed time resolved ZEKE photoelectron spectroscopy as a versatile tool for studying molecular dynamics

To support our experimental efforts we are utilizing extensive empirical, semi-empirical and ab initio chemical calculations.  This has been particularly useful in studying molecular conformations and vibrations associated with conformer interconversion dynamics.  Shown at the right is a calculation of a low frequency vibration in 9,10 dihydrophenanthrene which is one contributor to the inversion of the molecule through a planar transition state.

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Selected Publications

• "Laser Photoelectron Spectroscopy of 1- and 2-Naphthol: Relative Stability of the Cis and Trans Cation Rotamers" C. Lakshminarayan, J. M. Smith, J. L. Knee, Chem. Phys. Lett. 182, 656 (1991).
   
• "High Resolution Threshold Photoelectron Spectroscopy of Aniline and Aniline van der Waals Complexes" X. Zhang, J. M. Smith, J. L. Knee, J. Chem. Phys. 97, 2843 (1992).
   
• "Analysis of the Torsional Potential of 9,10-Dihydrophenanthrene in Three Electronic States: S₀, S₁ and the Cation Ground State" J. M. Smith, J. L. Knee, J. Chem. Phys. 99, 38 (1993).
   
• "Electronic Spectroscopy of Four Conformations of Jet-Cooled 1,6-Dihydroxynaphthalene" J. M. Smith, X. Zhang, A. Thompson, C. Lakshminarayan, J. L. Knee, J. Phys. Chem. 97, 3990 (1993).
   
• "Zero Electron Kinetic Energy Photoelectron Spectroscopy Using Picosecond Lasers" J. M. Smith, X. Zhang, J. L. Knee, Proc. Soc. Photo-Opt. Instrum. Engrs. 1858, 217 (1993).
   
• "Dynamics of High n Molecular Rydberg States with Application to Mass Analysed Threshold Ionization Spectroscopy" X. Zhang, J. M. Smith, J. L. Knee, J. Chem. Phys. 99, 3133 (1993).
   
• "Aniline-CH₄ S₁ Vibrational Dynamics Studied with Picosecond Photoelectron Spectroscopy" J. M. Smith, X. Zhang, J. L. Knee, J. Chem. Phys. 99, 2550 (1993).
   
• "Threshold Ionization Spectroscopy of the Low Frequency Vibrational Modes of Styrene and trans-Stilbene Cations" J. M. Smith, J. L. Knee, Laser Chemistry 14, 131 (1994).
   
• "Picosecond Vibrational Dynamics of Several S₁ Bands in Jet-cooled p-difluorobenzene" X. Zhang, J. M. Smith, J. L. Knee, J. Chem. Phys. 100, 2429 (1994).
   
• "Dynamics of Large Molecule van der Waals Complexes Studied with ZEKE Spectroscopy" X. Zhang, J. L. Knee, Faraday Discussion of Chem. Soc. 97, 299 (1994).
   
• "ZEKE Studies with Picosecond Lasers" J. L. Knee, in Highly Resolved Laser Photoionization and Photoelectron Studies, Current Topics in Ion Chemistry and Physics, T. Baer, C. Ng, eds., I Povis, Wiley, New York, (1995).
   
• "Time Resolved Threshold Ionization Spectroscopy" J. L. Knee, in Femtosecond Chemistry, J. Manz, L. Woste, eds., Verlag Chemie, New York, (1995).
   
• "IVR and Electronic Relaxation in the Channel Three Region of Benzene" J. M. Smith, X. Zhang, J. L. Knee J. Phys. Chem. 102, 1768 (1995).
   
• "Photoelectron Spectroscopy of Molecular Clusters" X. Zhang, J. Pitts, C. Zheng, J. L. Knee in Laser Techniques for State-Selected and State-to-State Chemistry III J. W. Hepburn, ed., Proc. SPIE 2548, 84, (1995).
   
• "Neutral and Cation Spectroscopy of Fluorene-Ar_n Clusters" X. Zhang, J. Pitts, J. L. Knee, J. Chem. Phys. 107, 8239 (1997).
   
• " Dynamics of Vibronically Excited Fluorene-Ar_n (n=4-5) Clusters", Jonathan D. Pitts and J.L. Knee, J. Chem. Phys., 108, 9632 (1998).
   
• "Electronic Spectroscopy and Dynamics of the Monomer and Ar_n Clusters of 9-Phenylfluorene", Jonathan D. Pitts and J.L. Knee, J. Chem. Phys., 109, 7113 (1998).
   
• "Conformational Energy and Dynamics of the S₁ State of 9-EthylFluorene", Jonathan D. Pitts, S. Wategaonkar and J.L. Knee, J. Chem. Phys., 110, 3378 (1999).
   
• " Vibrational Dynamics and Isomerization of 9-Ethylfluorene-Ar_n van der Waals Complexes", Jonathan D. Pitts and J.L. Knee, J. Chem. Phys 110, 3389 (1999).
   
• "Ethylindole Electronic Spectroscopy: S₁ and Cation Torsional Potential Surfaces" ,  Jonathan D. Pitts, Swarna Basu  and J.L. Knee, J. Chem. Phys., 113,  1857 (2000)
   
• "Conformational Studies of the Neutral and Cation of Several Substituted Fluorene" ,  Swarna Basu and J.L. Knee, J. Elect. Spect. And Related Phenomena, 112, 209 (2000).
   
• "Conformational Analysis and Dynamics of 9-Propylfluorene and 9-Ethylfluorene, Swarna Basu and J.L. Knee, J. Phys. Chem.,  A 105, 5842 (2001).
   
• "The Molecular Structure and Conformation of Cyclopropylbenzene as Determined by Ab Initio Molecular Orbital Calculations, Pulsed-Jet Fourier Transform Microwave Spectroscopic and Gas-Phase Electron Diffraction Investigations", Shen, Q., Wells, C. Traetteberg , M., Bohn, R.K., Willis, A., and Knee, J., J. Org. Chem., 66, 5840-5845 (2001).
   
• "Vibrational Dynamics of 9-Fluorenemethanol Using Infrared-Ultraviolet Double Resonance Spectroscopy", Swarna Basu and J.L. Knee, J. Chem. Phys., 120, 5631 (2004).
   
• "Conformational Analysis of Phenol Clusters using IR-UV Double Resonance Spectroscopy", in Preparation, Swarna Basu and J.L. Knee (2004).
   
• "Tryptophol Cation Conformations studied with ZEKE Spectroscopy", Quanli Gu, Swarna Basu, and J.L. Knee, J. Phys. Chem. A., 111 808 (2007)
   
• "Characterization of the dynamics of an essential helix in the U1a protein by time-resolved fluorescence measurements." Annunciado, D., et. al. Knee, J.L and Beveridge, D.L. J. Phys. Chem. B., 112 6122-30,  (2008).
   
• "Binding energies and dissociation pathways in the aniline-Ar2 cation complex." Gu, Q. and Knee, J.L., J. Chem Phys., 128(6) 064311 (2008).

  Education
  

  B.A. 1979 State University of New York, Binghamton

  Ph.D. 1983 State University of New York, Stony Brook

  

  
  [Chemistry] [Wesleyan]

  Last updated: July 16, 2009 (JLK/rncb)