|
| Bimolecular Interactions and Reaction Dynamics: |
Frequency and time-resolved laser spectroscopy and time-of-flight ion imaging methods
are implemented to accurately characterize inter-molecular potential
energy surfaces and the dynamics that occur on these surfaces.
Two moieties are first stabilized in a weakly bound complex by cooling the
species in a supersonic expansion. By cooling the complexes to
specific temperatures, we are able to stabilize the complexes with
preferred orientations between the constituents. The He···ICl(X,v=0)
complex, for instance, is found to have a T-shaped orientation at T ~ 5
K and at lower temperatures, T ~ 0.5 K, the complexes have preferred
linear geometries. These complexes serve as launching pads for
investigating the photo-induced dynamics that occur from these initial
orientations.
Thus far, systems such as He···ICl, Ne···ICl, H2···ICl, D2···ICl, He···Br2, He···I2, Ne···I2, Ar···I2, H2···I2, and D2···I2 have been investigated. A
close collaboration with Anne McCoy's group (Dept. of Chemistry, The Ohio State University), who performs high-level calculations of the ground- and excited-state interactions, enables the full picture of the interactions to be developed.
Related Publications:
"Photodissociation of the linear Ar-I2 van der Waals complex: velocity-map imaging of
the I2 fragment"
J. Chem. Phys. 130, 104302/1-104302/9 (2009)
"Probing the dependence of long-range, four-atom interactions on intermolecular
orientation: 2. Molecular deuterium and iodine monochloride"
J. Phys. Chem. A,
112, 9494-9502 (2008)
"Probing the dependence of long-range, four-atom interactions on intermolecular
orientation: 1. Molecular hydrogen and iodine monochloride"
J. Phys. Chem. A, 111, 13387-13396 (2007)
"Experimental and theoretical investigations of the He···I2 rovibronic spectra in
the I2 B–X, 20–0 region”
J. Chem. Phys., 125, 164314/1-164314/9
(2006)
|
"Spectroscopic identification of higher-order rare-gas-dihalogen complexes with different geometries: He2,3···Br2 and He2,3···ICl"
J. Phys. Chem. A, 112, 13393-13401 (2008)
"Spectroscopic identification of higher-order rare-gas-dihalogen complexes with different geometries: He2,3···Br2 and He2,3···ICl"
J. Phys. Chem. A, 112, 13393-13401 (2008)
"Stabilization of different conformers of weakly bound complexes to access varying excited-state intermolecular dynamics"
Adv. Chem. Phys., 138, 375-419 (2008)
|
|
|
Quantum-confinement Effects in 1-D
Semiconductor Nanoparticles: | A number of spectroscopy and microscopy techniques are utilized to determine how shape affects the optical properties of semiconductor quantum nanostructures. Specifically, we, in collaboration with the group of Professor Buhro, are investigating the dependence of band gap energies on the diameter of semiconductor nanowires. These nanowires are ideal for studying the two-dimensional quantum confinement of excitons since they can be synthesized with diameters as small as 3.5 nm and lengths on the order or microns. We are now using confocal microscopy coupled with cw and ultrafast laser to directly measure the exciton dynamics within individual nanowires. Both time-correlated single-photon counting and transient-absorption spectroscopy are utilized to monitor exciton dynamics in real time.
Related Publications:
"Origin of high photoluminescence efficiencies in CdSe quantum belts"
Nano Lett., 10, 352-357 (2010)
"Exciton localization and migration in individual CdSe quantum wires at low temperatures"
Phys. Rev. B, 80, 081303(R)/1-081303(R)/4 (2009)
|
|
|
|
Coherent Control of Chemical Dynamics:
|
|
|
Ultrashort laser pulses are used to initiate and
monitor the dynamics of molecules that can follow competing pathways.
Furthermore, the properties of the excitation pulse (amplitude and
phase) are manipulated to quantum mechanically control the yields of
the different product channels. A spatial light modulator coupled with
a genetic learning algorithm are used to achieve the desired outcome.
The ultimate goal here is to use the final properties of the excitation
pulse to gain insight into the details of the potential energy
surface(s) involved.
The coherent control of bimolecular reactions is also being pursued. Two reactants are stabilized in a non-reactive complex. A laser promotes the reactants above the barrier for reaction. The probability for reaction is then controlled by steering the reactants to specific intermolecular orientations and energies.
Coherent control via femtosecond pulse-shaping is also being utilized to steer exciton dynamics within semiconductor nanostructures, which are highly quantum-mechanical as a result of their dimensionality.
|
|
|
|
|