Cooperative Conduction Mechanisms Determined for Candidate Fuel Cell Electrolyte
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S. Trippel of the University of Freiburg in Germany, E. Hamilton at Northwestern University, and their colleagues have reported in the October 5, 2007 issue of Physical Review Letters (DOI:10.1103/ PhysRevLett.99.143602) an effective method to control the alignment and rotation of molecular objects using synchronized nanosecond and femtosecond laser pulses. The researchers also used quantum mechanical simulations to support their experimental findings on the efficacy of their method to align and manipulate molecules. Laser alignment of molecules results
from the interaction of the laser pulse with the dipole moment of the molecule. The research team employed a 10 nanosecond duration laser pulse to align molecules of 3,5 difluoroiodobenzene (DFIB) along its most polarizable axis (the axis defined by the bond between the C and I atoms). They then applied an orthogonally polarized 150 femtosecond duration pulse to activate motion about the aligned axis, resulting in rotation. The orientation and movement of the molecules was measured by monitoring ion fragments released from the molecules through pulsed excitation, as shown in Figure 1. By varying the length and
a
strength of the nanosecond and femtosecond alignment pulses, the researchers uncovered a parameter space within which the behavior of the molecule could be controlled. A numerical solution based on a nonperturbative solution of the Schrödinger equation of the molecular dipole and two laser fields provided a quantum mechanical basis for describing the behavior of the molecule. Though these experiments were carried out on 3,5 difluoroiodobenzene, the researchers generalized their model for an arbitrary molecular system. Furthermore, they expect, based on their numerical calculations, that by applying more sophisticated pulse sequences to the molecule, field-free alignment will be achieved. This method could prove fruitful for investigations exploring the rotational dynamics of complex molecules as well as for control of molecular torsions. ARTHUR FELDMAN
Cooperative Conduction Mechanisms Determined for Candidate Fuel Cell Electrolyte
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Figure 1: An overview of the laser pulse molecule alignment technique. (a) F+ ion imaging of 3,5 difluoroiodobenzene (DFIB) shows alignment in one and three dimensions, respectively, with the coordinate system shown in red. (b) Time-lapsed F+ ion imaging of DFIB shows the dephasing and revival of 3D alignment. (c) Stimulated rotation of the molecule, as measured by the expectation value of the angle of rotation about the tightly aligned molecular axis (cos 2) α, shown as a function of time after the short pulse. Reprinted with permission from Physical Review Letters 99 (2007) 143602. ©2007 by the American Physical Society.
MRS BULLETIN • VOLUME 33 • JANUARY 2008 • www.mrs.org/bulletin
Fuel cells are gaining increased attention recently as an efficient and clean method of generating electricity. An example is the solid-oxide fuel cell, where solid oxide refers primarily to the materials used for the electrolyte, and go
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