Chemical Physics and Physical Chemistry

Arnd Pralle, Buffalo; PChem Seminar

Thu, 2012-11-15 13:00 - 14:30
Location: 

Lynch Room

William Brennen

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First Name: 
William
Last Name: 
Brennen
Official Title: 
Emeritus Professor of Chemistry
Contact Information
Office Location: 
Senior Faculty Suite
Email: 
brennen2@sas.upenn.edu

Hendrik Hameka

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First Name: 
Hendrik
Last Name: 
Hameka
Official Title: 
Emeritus Professor of Chemistry

Physical Chemistry

Contact Information
Office Location: 
Senior Faculty Suite
Email: 
hameka@sas.upenn.edu

Mark Johnson, Yale; Physical Seminar - CANCELED

Thu, 2012-11-01 09:00 - 10:30

Location: Carolyn Hoff Lynch Room

Adam Wasserman, Purdue; Physical Seminar

Thu, 2012-10-11 09:00 - 10:30

Location: Carolyn Hoff Lynch Room

Connie Roth, Emory; Physical Seminar

Thu, 2012-10-04 09:00 - 10:30

Location: Carolyn Hoff Lynch Room

Michael R. Topp

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First Name: 
Michael R.
Last Name: 
Topp
Official Title: 
Professor of Chemistry

Physical Chemistry 

Contact Information
Office Location: 
249 N, Lab: 240 N
Email: 
mrt@sas.upenn.edu
Phone: 
(215) 898-4859
Admin Support: 
Education: 
  • B.Sc. Sheffield University (1966) - Haworth Medal winner
  • Ph.D. University College London and the Royal Institution of Great Britain (1969)
  • Member of Technical Staff, Bell Labs, (1969-71)
  • IBM Research Fellow, Pembroke College, Oxford (1971-73)
Research Interests: 

Conformational Relaxation in Isolated Molecular Clusters

When molecules become electronically excited, the rearrangement of electronic charge can precipitate many types of relaxation processes. To probe details of such events, one can employ isolated molecular clusters consisting of only a few hydrogen-bonded molecules. One particularly interesting case is the cluster involving a Coumarin 151 molecule bonded to a water dimer. Two different structures have been identified in the ground state, as shown below.

 

 

Recent experiments have shown that the species shown on the left here is unstable in the excited state, and relaxes to that shown on the right on a picosecond or nanosecond time scale depending on the available energy. This corresponds to movement of the water dimer by ~10Å from one side of the molecule to another, following and yet the activation energy is only 60 cm-1. Such conformational changes have been studied by a combination of fluorescence and infrared double resonance techniques in conjunction with ionization and mass resolution.

 

Hydrogen-Bonded Molecular Dimers

 

Hydrogen-bonded dimers present important opportunities to study short-range intermolecular interactions, including modification of the electronic structure, and corelated proton or hydrogen atom transfer. Molecules such as the dimer of 4-Amino-N-methylphthalimide, shown here, reveal dramatic changes in their infrared spectra between the ground and excited states. The simple ground-state ground-state infrared spectrum reflects the high symmetry of the ground state. On the other hand, the much more complex excited-state spectrum shows evidence for a loss of symmetry resulting from changes in the acid-base properties of NH2 and >C=O groups, which may result in proton transfer across the intermolecular hydrogen bonds. These types of strongly bonded dimers are different from many other dimer systems studied so far, because both their electronic and vibrational spectra are highly structured, despite the large increase in binding energy upon electronic excitation. Femtosecond-domain experiments are planned, to follow in real time the changes in vibrational spectra, which will provide further insights into the reasons for their complexity in the excited state.

 

 

Ultrafast Electronic Relaxation of Hydrogen-Bonded Molecules Studied by Femtosecond Pump-Probe Spectroscopy

 

Femtosecond pump-probe experiments allow us to observe the time evolution of the first events following pulsed laser excitation, including motions in the first coordination shell of a hydrogen-bonded molecule in fluid solution. New pump-probe experiments involving the detection of ultrashort-lived fluorescence have explored spectroscopic changes of aminophthalimide molecules in hydrogen-bonding solvents on a time scale more than 10 times faster than existing data for fluorescence Stokes shifts. Both fluorescence upconversion and pump-probe methods are being used to investigate ultrafast energy transfer processes in complex molecules, in collaboration with the Regional Laser and Biomedical Technology Laboratories at Penn.

Joseph Subotnik

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First Name: 
Joseph
Last Name: 
Subotnik
Official Title: 
Professor of Chemistry

Physical and Theoretical Chemistry

Contact Information
Office Location: 
268 Cret wing
Email: 
subotnik@sas.upenn.edu
Phone: 
215-746-7078
Admin Support: 
Education: 

B.A. Harvard University, 2000

Physics and Math (summa cum laude)


Ph.D.  UC Berkeley, 2006  Biophysics

 

NSF International Research Fellow (2007 -2009), Tel-Aviv

Postdoctoral Fellow, Northwestern University (2009-2010)

Research Interests: 

Research in the Subotnik group focuses on the intersection of static quantum chemistry methods (especially for excited states) with nonadiabatic dynamics methods (specifically surface hopping). The focus is quantifying electron transfer, energy transfer, and electronic relaxation. Applications are to almost all photo-induced processes!

Jeffery G. Saven

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First Name: 
Jeffery G.
Last Name: 
Saven
Official Title: 
Professor of Chemistry

Biological and Theoretical Physical Chemistry

Contact Information
Office Location: 
266 Cret, Lab 261 Cret
Email: 
saven@sas.upenn.edu
Phone: 
215-573-6062
Fax: 
215-573-2112
Admin Support: 
Education: 
  • BA, New College of Florida
  • PhD, Columbia University & University of Wisconsin
  • NSF Postdoctoral Fellow in Chemistry, University of Illinois, Urbana-Champaign, 1993-1995. Postdoctoral Research Associate, University of Illinois, Urbana-Champaign, 1995-1997
Research Interests: 

Computationally designed protein complex containing a nonbiological cofactor, designed and studied in collaboration with the DeGrado and Therien groups in the Department of Chemistry. On the left is the computationally designed protein scaffold (magenta) and two abiotic porphyrin cofactors (yellow). On the right is a model of the computationally designed sequence and structure.

 

Our research interests involve theoretical chemistry, particularly as it applies to biopolymers, macromolecules, condensed phases, and disordered systems. We are developing computational methods for understanding and designing molecular sytems having many physical and chemical degrees of freedom. Molecular simulation techniques are used both to study molecular systems in detail and to test and illustrate our theories. 

 

A current thrust of the group involves developing computational tools for understanding the properties of protein sequences consistent with a chosen three-dimensional structure. The group works closely with experimental groups at Penn and at other universities; some group members are involved in joint theoretical/experimental projects. Recent projects involve the design of soluble and membrane bound proteins, discerning the origins of conservation in naturally occurring proteins, biomolecular simulation, and the design of nonbiological folding molecules.

Andrew M. Rappe

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First Name: 
Andrew M.
Last Name: 
Rappe
Official Title: 
Blanchard Professor of Chemistry

Physical and Theoretical Chemistry

Additional Titles: 
Professor of Materials Science and Engineering
Co-Director, Pennergy
Contact Information
Office Location: 
264 Cret, Lab: 263, 265, 267, 268 Cret
Email: 
rappe@sas.upenn.edu
Phone: 
(215) 898-8313
Fax: 
(215) 573-2112
Admin Support: 
Education: 
  • B.A. Chemistry and Physics, Summa Cum Laude, Harvard University (1986)
  • ONR Graduate Fellow, Massachusetts Institute of Technology (1986-1989)
  • JSEP Graduate Fellow, Massachusetts Institute of Technology (1990-1992)
  • Ph. D. Physics and Chemistry, Massachusetts Institute of Technology (1992)
  • IBM Postdoctoral Fellow, University of California at Berkeley (1992-1994)
  • Assistant Professor of Chemistry, University of Pennsylvania (1994-2000)
  • Associate Professor of Chemistry, University of Pennsylvania (2000-2006)
  • Professor of Chemistry, University of Pennsylvania (2006-present)
  • NSF CAREER Award (1997-2001)
  • Alfred P. Sloan Foundation Fellow (1998-2000)
  • Dreyfus Teacher-Scholar Award (1999-2004)
Research Interests: 

 

My research group creates and uses new theoretical and computational approaches to study complex systems in materials science, condensed-matter physics, and physical chemistry.

 

We look for new phenomena that occur when different components are brought together. For example, we examine molecules adsorbing on metal surfaces, in order to understand the effect of surface composition and structure on preferred adsorption sites, dissociation pathways, and vibrational dynamics. We also study how the compositions of oxide solid solutions lead to Angstrom-scale chemical structure, nanometer scale structural disorder, and long-range ferroelectric and piezoelectric properties. These studies find real-world applications in catalysis, corrosion, SONAR, fuel cells and other important technologies. Whenever possible, we model systems analytically, in order to extract general principles and simple pictures from complex systems. We recently derived general expressions for the vibrational lifetimes of molecules on surfaces, revealing the dependence of lifetime on molecular coverage and arrangement. Our recent exploration of quantum stress fields has helped to link chemical and mechanical effects in materials.

 

We are constantly developing methods for computing new properties, and for making quantum-mechanical calculations more accurate and more efficient. We tailor computational algorithms to maximize performance on modern computing platforms such as Beowulf clusters. Wherever possible, we also model systems analytically, in order to extract general principles and simple pictures from complex systems. This combination of theoretical and computational tools enables us to identify new phenomena in complex systems, like multicenter bonds between methyl radicals and the rhodium surface. ( See figure below )

Converting the 5d wavefunction of gold to a smoother pseudowavefunction results in a dramatic reduction in the required basis set size for converged calculations.

Department of Chemistry

231 S. 34 Street, Philadelphia, PA 19104-6323

215.898.8317 voice | 215.573.2112 fax | web@chem.upenn.edu

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