|
Associate Professor, Physical Chemistry
B.S. 1991, St. John's University
Ph.D. 1996, North Dakota State University
Postdoctoral: 1996-1998, Columbia University
Email: quandt@ilstu.edu
Phone: (309)438-8576
Office: 324 Science Laboratory Building
My research
entails using Cavity Ringdown (CRD) absorption spectroscopy to
study the kinetics and dynamics of gas phase reactions that are
important in both atmospheric and combustion chemistry.
CRD
Currently, the most commonly used methods of measuring
electronic spectra of gas phase molecules are LIF and REMPI.
While often quite successful for small systems, they are
problematic for larger polyatomics due to dynamical processes
such as internal vibrational redistribution (IVR), internal
conversion (IC), and predissociation. In these cases a direct
absorption measurement is preferable, but often not practical
due to low sensitivity. One solution is the use of a novel
multipass absorption method termed "cavity ringdown".
A CRD cell is essentially a
high-quality optical cavity enclosed by a pair of highly
reflective mirrors. Pulsed laser light from a Nd:YAG pumped dye
laser that is injected into the cavity oscillates between the
mirrors with a small amount (1-R) transmitting on each pass. If
the transmitted light is monitored at the output mirror as a
function of time, the decay time of the cavity can be
determined. The intensity at the output mirror is given by I(t)
= Ioe-t/t
where t is
the "ringdown" time, that is, the time for the signal
to decay to 1/e of Io. If an absorbing species is
placed between the cavity mirrors, the ring down time is
shortened. The total round trip loss G,
due to absorption, is then G
= 1-e-2L/ct. A plot of G
versus wavelength gives the absorption
spectrum for the species of interest. The sensitivity of this
technique is limited by the reflectivity of the mirrors, and the
precision with which t
can be determined. Under the right conditions, an effective path
length of up to 70 km is possible, and absorptions with cross
sections on the order of 10-28 cm2 can be
seen.
HFCs and HCFCs
It has been shown conclusively that the use of
chlorofluorocarbons (CFCs) as refrigerants, aerosol propellants,
and etchants, in semiconductor manufacturing, has significantly
contributed to stratospheric ozone destruction. (The "ozone
hole") Since 1987, the search for suitable alternatives to
CFCs has centered on hydrochlorofluorocarbons (HCFCs) and
hydrofluorocarbons (HFCs). These compounds’ environmental
acceptability stems from the fact that the presence of one or
more C-H bonds allows them to be oxidized relatively quickly by
OH radicals in the troposphere. This gives HCFCs and HFCs a mean
atmospheric lifetime on the order of 3 to 6 months as opposed to
the decade long lifetimes associated with CFCs. However, because
of various atmospheric phenomenon, some of these HCFCs can reach
the stratosphere. Therefore, to determine the impact of these
compounds on the ozone layer detailed knowledge of the UV and
VUV photochemistry of CFCs and HCFCs is needed. In our lab, we
study the photodissociation dynamics of several different HCFCs.
This is done by flash photolysis using an ArF excimer laser
operating at 193 nm to photodissociate the species of interest,
and the CRD technique to probe the energy distribution of the
photoproducts.
Combustion Chemistry
Combustion of fossil fuels is the most commonly used
method of energy production in the world today. Reactions of O(3P)
with alkenes are key intermediate steps in the combustion
chemistry of these fossil fuels. Despite the importance of these
types of reactions very little work has been done on systems
larger than O(3P) + C2H4. In
our lab we want to measure the energy distribution of various
reaction products from O(3P) reactions with alkenes,
in specific we are interested in the HCO product. Due to its
unique electronic structure HCO is difficult to detect using
traditional techniques. However, it is relatively easy to detect
using CRD.
|
|
SELECTED PUBLICATIONS
E.D. Tweeten, B.J. Petro, R. W. Quandt,
Formation of Molecular Iodine from the Two Photon Dissociation of CI4
and CHI3: An Experimental and Computational Study,
Journal of Physical Chemistry A, 107 (2003) 19-24
S.A. Drake, J.M. Standard, R.W. Quandt,
"An Ab Initio Investigation of the Ground and Excited Electronic
State Properties of a Series of Bromine and Iodine-Containing Singlet
Carbenes," Journal of Physical Chemistry A, 106 (2002)
1357-1364.
Z. Min, R.W. Quandt, T.H.Wong, R. Bersohn,
The CO Product of the Reaction of O(3P) with CH3
Radicals." Journal of Chemical Physics, 111 (1999)
7369-7372.
Z. Min, T.H. Wong, R.W. Quandt, R. Bersohn,
"The Reactions of O(3P) with Alkenes: The Formyl Radical
Channel." Journal of Physical Chemistry A, 103 (1999)
10451-10453.
Z. Min, R. Quandt, R. Bersohn,"Kinetic
Energies of Hydrogen Atoms Photodissociated from Alkyl Radicals," Chemical
Physics Letters, (1998) 372-376.
|
