Physical Chemistry: Molecular Spectroscopy utilizing a variety of techniques including Resonance Enhanced Multiphoton ionization, Zero Electron Kinetic Energy (ZEKE) photoelectron spectroscopy, Mass Analyzed Threshold Ioniztion (MATI) spectroscopy, and IR-UV double resonance spectroscopy. In addition a variety of computational chemistry methods are utilized. These experimental and computational techniques are applied to the study of isolated, gas phase large molecules and clusters.
The recent focus of our research has been on studying the detailed interactions which determine conformational structure in large molecules and molecular clusters including the evolution of structure associated with dynamical process such as conformational interconversion and dissociation. Our primary approach is experimental measurement of isolated gas phase molecules and clusters using a variety of laser spectroscopic techniques. These include excited state vibronic spectroscopy using resonance enhanced multi-photon ionization (REMPI), ground and excited state vibrational spectroscopy using ultra-violet Infrared (UV-IR) double resonance spectroscopy and cation vibronic spectroscopy using zero electron kinetic energy (ZEKE) spectroscopy. The diversity of techniques used allows us to map out the molecular conformations and dynamics in several electronic states helping to unravel how electronic excitation influences the molecular properties. In support of these experimental studies we have been utilizing increasingly sophisticated quantum chemical calculations to give a more complete picture of the molecular structure and dynamics.
The following are several recent projects:
Aniline-Arn dissociation pathways. One of molecular properties which is difficult to accurately measure is the dissociation energy. In this work we used Mass Analysed Threshold Ionizaton (MATI) spectroscopy to accurately measure the dissociation energy of one and two Ar atoms bound to Aniline. An unexpected low energy dissociation pathway for Aniline-Ar2 in the cation was revealed and led to the identification of a new local minimum for the Aniline-Ar in the cation. Link to Publication
Accurate Determination of a water-carboxylic acid binding energy
Using an IR-UV double resonance technique we have been able to accurately measured the binding energy of a carboxylic acid (9-hydroxy fluorine carboxylic acid – 9HFCA) to water with an accuracy of better than 0.1 kcal/mole. A subsequent paper focused on the interaction of multiple hydrogen bonds within clusters of 9-HFCA with a series of smaller acid binding partners. In 9-HFCA the 9-hydroxy is internally H-bound to the carbonyl oxygen. When dimers of 9-HFCA are formed, through two additional intermolecular H-bonds, the strength of the internal 9-hydroxy bond is changed. This change was monitored via IR spectroscopy and was found to report very accurately on the nature of the intermolecular bonds. Extensive quantum chemical calculations were performed to model these effect and a correlation was observed between the measured 9-OH frequency and the calculated Natural Bond Orbital (NBO) sigma* population. Calculations were also performed on a number of model systems including the much simpler, but related, glycolic acid. Link to Publication
Recent Publications: ( Full List of Publications )
Infrared spectroscopy of gas phase alpha hydroxyl carboxylic acid homo and hetero dimers, Quanli Gu, Yong Xia, Sifeng Chen, Peifeng Su, Zhijun Yang, Carl Trindle and J. L. Knee, Phys. Chem. Chem. Phys., DOI: 10.1039/C8CP05979A (2018)
Quantitative probing of subtle interactions among H-bonds in alph hydroxyl carboxylic acid complexes, Quanli Gu, Peifeng Su, Y. Xia, Zhijun Yang, Carl Trindle and J. L. Knee, Phys. Chem. Chem. Phys., 19(36) 24399 (2017). DOI: 10.1039/C7CP03917D
Communication: Physical origins of ionization potential shifts in mixed carboxylic acids and water complexes, Quanli Gu, Zhen Tang, Peifeng Su, Wei Wu, Zhijun Yang, Carl Trindle, and Joseph Knee, J. Chem. Phys. 145, 051101 (2016) http://dx.doi.org/10.1063/1.4959970
Influences of the propyl group on the van der Waals structures of 4-propylaniline complexes with one and two argon atoms studied by electronic and cationic spectroscopy, Zhijun Yang, Quanli Gu, Carl O. Trindle, and J.L. Knee, J Chem Phys, 143, 034308 (2015). http://dx.doi.org/10.1063/1.4927004
Electronic and Cationic Spectroscopy of 9-Hydroxy-9-fluorene Carboxylic Acid, Quanli Gu, Carl. O. Trindle, J.L. Knee, J Phys Chem A, 118, 4982 (2014), doi: 10.1021/jp5045578
Communication: The ionization spectroscopy of mixed carboxylic acid dimers, Zhijun Yang, Quanli Gu, Carl O. Trindle, and J. L. Knee, J. Chem. Phys. 139, 151101 (2013). doi:10.1063/1.4825381
HU Induced Perturbation to the Structure and Dynamics of Flexible DNA, T. Moreno, I. Mukerji and J. L. Knee Biophysical Journal 104(2) 422A (2013); doi: 10.1063/1.4825381.
Zero kinetic energy photoelectron spectroscopy of tryptamine and the dissociation pathway of the singly hydrated cation cluster, Quanli Gu and J. L. Knee, J. Chem. Phys. 137, 104312 (2012). doi:10.1063/1.4752080
Communication: Frequency shifts of an intramolecular hydrogen bond as a measure of intermolecular hydrogen bond strengths, Quanli Gu, Carl Trindle and J. L. Knee, J. Chem. Phys., 137, 091101 (2012).
Applying 6-Methylisoxanthopterin-Enhanced Fluorescence To Examine Protein–DNA Interactions in the Picomolar Range, Andrew Moreno, Joseph Knee, Ishita Mukerji, Biochemistry, 51, 6847 (2012), doi: 10.1021/bi300466d
Communication: Spectroscopic measurement of the binding energy of a carboxylic acid-water dimer Quanli Gu and J. L. Knee, J. Chem. Phys. 136, 171101 (2012); doi: 10.1063/1.4711862
B.A. 1979 State University of New York, Binghamton
Ph.D. 1983 State University of New York, Stony Brook
Recent Research Students
Andrew Moreno, Ph.D., 2014
Swarna Basu, Ph.D. 2002