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potential-energy surfaces)
potential-energy surfaces Daniel
A. Brue, Xuan Li, and
Gregory A.
Parker
Department
of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma
73019
We
have calculated new potential-energy surfaces for the lowest
two spin-aligned 4A
states of the Li3 trimer. This calculation shows a
seam of conical intersections between these states resulting
from the extra symmetry of the system when the atoms are
in a collinear arrangement. This seam is especially
important because of its proximity to the three-body
dissociation limit of the system; ultracold scattering
calculations and the bound-state energies of the system will
be affected by the presence of this conical intersection. In
this paper we discuss the calculation of the potential-energy
surface and the location of the conical intersection
seam
link: J.
Chem. Phys. 123, 091101 (2005)
Xuan
Li , Daniel A. Brue,
and Gregory A.
Parker
Department
of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma
73019
This paper develops the general theory for laser fields interacting
with bimolecular systems. In this study, we choose to use the
multipolar gauge on the basis of gauge invariance. We consider both
the adiabatic and nonadiabatic cases and find they produce similar
interaction pictures. As an application of this theory, we present
the study of rovibrational energy transfer in Ar + CO collisions in
the presence of an intense laser field.
link: J.
Phys. Chem. A, 110 (16), 5504 -5512, (2006)
)
potential energy surface
Xuan Li, Daniel
A. Brue,and Gregory A.
Parker
Department
of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma
73019
In this paper,
we present a calculation for the bound states of A1 symmetry on the
spin-aligned Li3(4A)
potential energy surface. We apply a mixture of discrete variable
representation and distributed approximating functional methods to
discretize the Hamiltonian. We also introduce a new method that
significantly reduces the computational effort needed to determine
the lowest eigenvalues and eigenvectors (bound state energies and
wave functions of the full Hamiltonian). In our study, we have found
the lowest 150 energy bound states converged to less than 0.005%
error, and most of the excited energy bound states converged to less
than 2.0% error. Furthermore, we have estimated the total number of
the A1 bound states of Li3 on the spin-aligned Li3(4A)
potential surface to be 601.
link: J.
Chem. Phys. 127, 014108 (2007)
Xuan
Li, Gregory A. Parker,
Paul Brumer^1 , Ioannis Thanopulos^2 and Moshe
Shapiro^{2,3}
Department
of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma
73019
1Department of Chemistry and Center for Quantum Information and Quantum Control, University of Toronto, Canada
2Department of Chemistry, The University of British Columbia, Vancouver, Canada
3Department of Chemical Physics,
The Weizmann Institute, Rehovot, Israel
We present a
non-perturbative time-dependent quantum mechanical theory of the
laser catalysis and control of a bifurcating $
A+BC\stackrel{\hbar\omega_0}{\longleftrightarrow} ABC^*(v)
\stackrel{\hbar\omega_0}{\longleftrightarrow} AB+C $ reaction, with
$ABC^*(v)$ denoting an intermediate, electronically-excited, complex
of $ABC$ in the $v$-th vibrational state. We apply this theory to the
low collision energy fermion-boson light-induced exchange reaction,
$^6{\rm Li}(^2S)+$ $^7\textrm{Li}_2(^3\Sigma_u^+)
\stackrel{\hbar\omega_0}{\longleftrightarrow}(^6{\rm Li}^7{\rm
Li}^7{\rm Li})^* \stackrel{\hbar\omega_0}{\longleftrightarrow}$
$^6{\rm Li}^7\textrm{Li} (^3\Sigma^+)+^7\textrm{Li}(^2S).$ We show
that at very low collision energies and energetically narrow ($\sim
0.01$ cm$^{-1}$) initial reactant wave packets, it is possible to
tune the yield of the exchange reaction from 0 to near-unity (yield
$\geq 99\%$) values. Controllability is somewhat reduced at
collisions involving energetically wider ($\sim1$ cm$^{-1}$) initial
reactant wave packets. At these energetic bandwidths the radiative
reactive control, though still impressive, is limited to the $0 -
76\%$ reactive-probabilities range.
link: J.
Chem. Phys. 128 124314, (2008)
We show that by using laser catalysis, we can employ translationally cold (Tr1.75 K) collisions to produce ultracold (0.01 mK<Tp<1 mK) (homonuclear) molecules. We illustrate this approach by studying the laser catalysis of the 6Li+6Li7Li(6Li6Li7Li)*(14A)6Li6Li+7Li reaction in the collinear approximation. Ultracold 6Li6Li product molecules are shown to be produced at an extraordinary yield of up to 99.97%, using moderate laser intensities of I=100 kW/cm2-10 MW/cm2.
link: Phys. Rev. Lett. 101, 043003 (2008)
Xuan Li
and Gregory A. Parker
Department of Physics and Astronomy, University of Oklahoma,
Norman, Oklahoma 73019
We present a new theory of population transfer by adiabatic passage. This theory relates laser catalysis to adiabatic passage, enhancing chemical reactions with the freedom to choose the translational energies of the reactants and products separately. The process, $ A+BC\stackrel{\hbar\omega_p}{\longleftrightarrow} ABC^*(v) \stackrel{\hbar\omega_s}{\longleftrightarrow} AB+C$, involves two laser fields which are slowly varying so the process is adiabatic, and sufficiently intense so the population of the intermediate bound complex ($ABC$) is minimized. We apply this theory to the collinear exchange reaction $^6$Li$+$ $^7$Li$_2(T_r$) $\stackrel{\hbar\omega_p}{\longleftrightarrow}(^6$Li$^7$Li$^7$Li$)^* \stackrel{\hbar\omega_s}{\longleftrightarrow}$ $^6$Li$^7$Li$(T_p$)$+^7$Li. We show that at translational energies $T_p=T_r=1$ mK with a narrow energy bandwidth of $\delta_E=0.01$ mK, we can obtain nearly total ($\geq 98 \%$) population transfer from the reactant to the product states. This can be done with a pump laser and a Stokes laser in an ``intuitive'' sequence ($t_p<t_s$) at a low intensity ($I_p\leq 600$MW/cm$^2$) and a ``coincident'' sequence ($t_p=t_s$) at a higher intensity.
link: J. Chem. Phys. 128 184113, (2008)
Global potential energy surfaces for the 1 4A', 2 4A', 1 4A", and 2 4A" spin-aligned states of Li3 are constructed as sums of a diatomics-in-molecules (DIM) term plus a three-body term. The DIM model, using a large basis set of 15 4A' and 22 4A' states, is used to obtain a “mixed-pairwise additive” contribution to the potential. A global fit of the three-body terms conserves the accuracy of the ab initio points of a full configuration-interaction calculation. The resulting fit accurately describes conical intersections for both the 1 4A' and 2 4A' surfaces with a root-mean-square (rms) deviation of 5.4×10−5 hartree in Dih geometries and 1.2×10−4 hartree in Civ geometries. The global fit appears to be quantitatively correct with a rms deviation of 1.8×10−4hartree for 1 4A', 9.2×10−4 hartree for 2 4A', 2.5×10−4 hartree for 1 4A", and 5.1×10−4 hartree for 2 4A". A possible diabolic conical intersection, also called an accidental degeneracy, in C2v geometries, indicating a seam of conical intersections in Cs geometries, is also found in ab initio calculations for A2 states. As shown in this example, the DIM procedure can be optimized to describe the geometric phase and nonadiabatic effects in multisurface potentials.
link: J.
Chem. Phys. 129, 124305 (2008)