DAVIS
GROUP- MOLECULAR REACTION DYNAMICS
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260,262,263
Spencer T. Olin Laboratory |
Welcome...
This is the Davis Group homepage in the Department of Chemistry and Chemical Biology at Cornell University.
Click here for a live view of the Campus.
The objective of our research is to understand the mechanisms for elementary chemical reactions relevant to catalytic processes, combustion, and atmospheric chemistry. Highly reactive species such as transition metal atoms, clusters, free radicals, and aerosol particles are prepared in molecular beams. Using crossed molecular beams and various laser techniques, we conduct experimental studies of chemical reactions resulting from single bimolecular collisions between reactant atoms or molecules. Much of the information is derived from measurements of product angular and velocity distributions as a function of collision energy and reactant quantum state. Check out our Publications Page to see what we have been doing...
Our research is currently supported by the National Science Foundation, and the U.S. Department of Energy. Over the years, we have also been supported by the ACS Petroleum Research Fund, and the Alfred P. Sloan Foundation.
Over the past couple of years, we have devoted great effort to the development of high intensity VUV sources based on 4-wave mixing of collimated (unfocused) laser beams. This produces intensities that are one to three orders of magnitude higher than most other methods. We use this for producing 10 eV radiation for “soft” photoionization of products from crossed molecular beams reactions using a rotatable source apparatus, shown below.
In earlier work, we employed 7.9 eV (157nm) light from a F2 excimer laser, which was well-suited for transition-metal containing molecules which have low ionization energies. With our new 10 eV source (125 nm), we are now able to study reactions of polyatomic free radicals (e.g., C6H5 + O2), or reactions of transition metal atoms having higher ionization energies (Pt + CH4), or isotope exchange reactions of partially ligated transition metal complexes (e.g., C5H5CoH2 + C3H6). For more information, follow this link
Our ultrabright VUV source at 130 nm improves our sensitivity in oxygen atom Rydberg tagging TOF (ORTOF) spectroscopy, a method developed in our laboratory, by at least several orders of magnitude. In this case, three input laser beams for VUV generation by four-wave mixing are each tuned near atomic resonances in the nonlinear medium. By combining this method with the use of narrowband lasers, we have reached the point where the first true crossed beam study of the H + O2 -> OH + O reaction is possible.
In the photos below, Dan Albert is working on the Rydberg O atom Machine. Three tunable dye lasers (Scanmates) are used to produce the 130nm VUV light, and a fourth laser in foreground (Lumonics) is used to excite the O(3S) to a high-n Rydberg state. The crossed beams machine is at the right edge of the photo below.
Dan standing in front of the rotatable detector crossed beams apparatus.
For many years, we have employed laser vaporization sources to produce beams containing transition metal atoms and clusters for studies of C-H and C-C bond activation of hydrocarbon molecules. For production of extreme UV radiation at wavelengths shorter than the LiF cutoff (104nm), windowless operation is required. Michael Todt has recently set up a new windowless 4-wave mixing apparatus employing pulsed laser vaporization to produce the metallic vapor used for 4-wave mixing. This approach, combined with noncollinear phasematching, facilitates production of high intensity pulses above 12eV, making it possible to do "soft" photoionization of nearly any molecular species of interest. Below are two photos of Michael in the laboratory working on the XUV light source.
In an effort to make chemistry and
physics instrumentation available to high school and introductory college
chemistry and physics classes, we have developed simple spectrophotometers that
can be constructed using readily available parts at extremely low cost
($25). One design is constructed using
Lego® blocks, a light emitting diode, and optical elements including
a lens, slide-mounted diffraction grating, and photodiode detector. The photodiode detector is mounted on a
rotatable arm for wavelength selection based on simple laws of
diffraction. The design is extremely
simple, thereby demonstrating basic physical principles (such as diffraction
and absorption of light) that are frequently lost in commercial “black box”
instruments. Performance, measured by
comparison to a commercial spectrometer, is sufficiently quantitative to
facilitate experiments such as the determination of the pKa
of an acid-base indicator! Click here for more
information.
Research:
- Crossed Beam Studies Using Ultrabright Tabletop VUV Light Source
- Vibrational vs. Translational Energy in Promoting Transition Metal C-H Insertion
- Transition Metal Chemistry in Crossed Beams
- Building a Crossed Molecular Beams Apparatus
- Crossed Beams Studies of Free Radical Reactions
Current Group Members:
- Prof. H. Floyd Davis
- Daniel Albert
- Michael Todt
- Alumni:
- David Proctor Ph.D. Cornell (2009)
- Steve Kroner (Ph.D. jointly with B. Carpenter).
- Marivi Ortiz-Suarez., Ph.D. Cornell (2006)
- Yumiko Nakatsuka, MSc. Cornell (2005)
- Melania Oana, Ph.D. Cornell (2005) (Ph.D. jointly with R. Hoffmann)
- Mark Witinski, Ph.D. Cornell (2005)
- Jon Schroden, Ph.D., Cornell (2003)
- Cheng Lin, Ph.D., Cornell (2002).
- Ryan Hinrichs, Ph.D., Cornell (2001).
- Brian Strazisar, Ph.D., Cornell (2000).
- Hans Stauffer, Ph.D., Cornell (2000).
- Peter Willis, Ph.D., Cornell (1999).
- Eugene Bernard, Ph.D., Cornell (1997).
Publications:
Visit our Publications Page
containing a listing of selected publications from members of the group.
Back to Department of Chemistry and
Chemical Biology
Courses:
Information for Prospective Graduate
Students:
Several different projects are available for graduate students from the incoming class. At least two openings are available. For information about our future research plans, contact Floyd Davis at hfd1@cornell.edu
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Please, direct any comments, questions, or
problems regarding this web site to Floyd
Davis