George Lynn Cross Research Professor, Professor Emeritus
Over the years we have developed theoretical and numerical methods for accurately studying three-particle systems of real physical interest. Our reactive scattering theory, hyperspherical coordinates, and discrete variable representation has allowed us and others to solve the Schrödinger equation with minimal approximations. In addition we have also developed rotational decoupling approximations which are widely used in atom-diatom inelastic scattering and has led to ultrasimple expressions for calculating integral and differential cross sections.
We have studied a variety of systems including: Positronium formation which occurs when a positron collides with a Hydrogen atom. Positronium is an exotic atom composed of a positron-electron pair. The highly exoergic F+H2 reaction is an important bottle neck step in powerful hydrogen fluoride lasers. We also studied the single most important combustion reaction H+O2. This reaction is the rate limiting step which determines rates of explosion and flame propagation.
Currently, we are interested in ultracold collisions of alkali atoms with alkali dimers. This interest is the result of the phenomenal success in the experimental formation of ultracold atoms and molecules. We have recently shown that pulsed lasers of moderate intensities used during the collision can lead to the efficient production of ultracold molecules. This laser catalyzed production of ultracold molecules utilizes a laser to quantum mechanically control the chemical reaction. This is accomplished by forcing a virtual transition of the reactants to an excited state complex. Then the excited state complex undergoes stimulated emission back to the ground electronic state, releasing a photon identical to the absorbed photon.
Another reason for the interest in triatomic Li3 is the existence of energetically accessible conical intersections in both the doublet and quartet states. A conical intersection is seen where two different Born-Oppenheimer electronic states intersect. The presence of conical intersections affect the bound states of Li3 and the Li+Li2 dynamics.
"Pulse Sequences in Photoassociation via Adiabatic Passage," X. Li, W. Dupre, G.A. Parker, New J. Phys., 14, 073001, (2012) ADS: 2012NJPh...14g3001L
"Geometric Phase for Collinear Conical Intersections. I. Geometric Phase Angle and Vector Potentials," X. Li, D.A. Brue, B.K. Kendrick, J.D. Blandon and G.A. Parker, J. Chem. Phys., 134, 064108, (2011) ADS: 2011JChPh.134f4108L
"Laser-Catalyzed Production of Ultracold Molecules: The 6Li+6Li7Li + ℏ ω → 6Li2+ 7Li Reaction," X. Li, G.A. Parker, P. Brumer, I. Thanopulos and M. Shapiro, Phys. Rev. Lett., 101, 043003, (2008) ADS: 2008PhRvL.101d3003L
"Potential Energy Surfaces for 14A’, 24A’, 14A”,24A” States of Li3. Use of Diatomics in Molecules to Fit Full Configuration Interaction Data," X. Li, D.A. Brue, and G.A. Parker, J. Chem. Phys., 129, 124305, (2008) ADS: 2008JChPh.129l4305L
"Theory of Laser Enhancement of Ultracold Reactions: The Fermion-Boson Population Transfer Adiabatic Passage of 6Li+6Li7Li(Tr = 1mK) ⇌ 6Li2 + 7Li(Tp =1mK)," X. Li and G.A. Parker, J. Chem. Phys., 128, 184113, (2008) ADS: 2008JChPh.128r4113L
"Theory of Laser Enhancement and Supression of Cold Reactions: The Fermion-Boson 6Li+7Li2 ⇌ 6Li7Li + 7Li Radiative Collision," X. Li, G.A. Parker, P. Brumer, I. Thaanopulos and M. Shapiro, J. Chem. Phys., 128, 124314, (2008) ADS: 2008JChPh.128l4314L