My research has been in the area of high-resolution spectroscopy and its applications to analysis of molecular dynamics.

A key part of my work was the development of all-optical high-resolution continuous wave triple resonance spectroscopy.  This work was done in collaboration within the group of  Profs. William C. Stwalley and Paul Kleiber at the University of Iowa.  It was initially used for high resolution spectroscopy at intermediate internuclear distance, a region not accessible from the thermally populated part of the electronic ground state.  It was also used in state-selective photo-dissociation dynamics experiments at that time.

Since 1991, our research group at Temple University has continued fundamental photophysics and photochemistry studies in a state-of-the-art continuous wave Laser Facility.  Our research group has used these high resolution techniques to study coherence and quantum interference effects such as Electromagnetically Induced Transparency and Autler-Townes splitting in open molecular systems.  We have demonstrated that these effects can be used to control molecular angular momentum alignment and quantum state character (singlet-triplet mixing).  Profs. Lorenzo Narducci (Drexel University) and Frank Spano (Temple University) have supported the development of theoretical methods needed for the simulation and analysis of these quantum interference effects.

In addition, our group has shown that the Autler-Townes effect can be used to measure the absolute value of the molecular transition dipole moment and its inter nuclear distance dependence.  In this case an accurate measurement of the coupling laser E field amplitude together with the simulation of the Autler-Townes split line shape yields the absolute value of this fundamentally important molecular parameter.  This method can also be used to normalize relative experimental (fluorescence based) or theoretical ab initio transition dipole moment values to an absolute scale. Such efforts are in progress in collaboration with Prof. John Huennekens (Lehigh University).

Our group has also recently developed a new four-color  high-resolution laser spectroscopic technique (quadruple resonance), which provides enhanced flexibility in these studies at increasingly larger inter nuclear distance values through multiple excitation steps.

Recent developments in cold atom/molecule photoassociative spectroscopy involving the large inter nuclear distance regime have resulted in a widespread interest in producing ultracold ground state molecules. The photoassociation and Raman transfer steps used in these experiments require accurate knowledge of the excited states energy level structure.  The lowest excited states also provide the most widely used pathways to higher lying excited states for characterization of ultracold molecules, for example.  Accurate knowledge of the energy level structure and the quantum state character of the mixed singlet–triplet rovibronic eigenstates is of special interest for identification of the most optimal excitation pathways to reach the ‘dark’ excited triplet states, which are not accessible from the singlet ground state.  Our collaboration with Dr. Tom Bergeman at Stony Brook, Prof. Li Li at Tsinghua University and Dr. Amanda Ross in Lyon, France, on the global analysis of the lowest electronic states in K2 and Na2 has resulted in an ‘accurate road map’ to the excited states in these molecules. The analysis has dealt with questions such as how to model spin-orbit functions and Born-Oppenheimer potentials including the exchange and dispersion terms.  These studies are of inherent interest, because the nonadiabatic couplings between the various closely spaced electronic states dominate processes such as bond-breaking photodissociation and bond-forming associative ionization.

Since molecular formation dynamics is encoded in the energy of the molecular eigenstates, high-resolution spectroscopy is a beautiful way of learning about dissociation and collision dynamics. Based on spectroscopic data alone, determination of these potentials will also allow calculations of collision cross sections and the scattering length as well as atomic line broadening parameters and long range interaction coefficients.