Please join us for an informal seminar sponsored by the Atomic and
Molecular Physics Division, Harvard-Smithsonian Center for Astrophysics.
(Complete schedule at
http://www.cfa.harvard.edu/amp/events.html)
2:00 PM Monday March 28, 2011
PRATT Conference Room
60 Garden St., Cambridge, MA 02138
Non-Born-Oppenheimer effects in the F/Cl+H2 reactions at
thermal and hypothermal energies
Professor Millard Alexander
Dept. of Chemistry and Biochemistry
and Institute for Physical Science and Technology,
University of Maryland
Because of its experimental accessibility, the reaction of F with
H2 and its isotopomers has long been the paradigm for exothermic
triatomic reactions. Our previous work has demonstrated that as the
collision energy decreases and the Born-Oppenheimer allowed reaction
of F(2P3/2) becomes suppressed by the reaction barrier, BO forbidden
reaction of the more energetic spin-orbit excited atom becomes
increasingly important. [1-3].
Reactions at low collision energy are of importance in astrophysics
and are increasingly relevant as experimental techniques for cooling
molecules grow more sophisticated. Investigations of the F+H2
reaction at very low collision energy using just the lowest FH2 PES
have predicted a large increase in the reaction cross section and
a comparable increase in the reaction rate constant. [4]
In this talk we investigate the role of non-BO pathways in the F+H2
reaction at collision energies down to <= 10-4 eV, making use of
our multiple-PES formalism. [1] As we shall show, at low energy the
BO-forbidden reaction of the spin-orbit-excited atom (F*) dominates.
Also, reaction of F* is greatly enhanced by resonances associated
with quasi-bound H+HF(v=3, j=2, 3,4) complexes which are nearly
degenerate with the F*+H2(v=0, j=0) channel.
The potential energy surfaces are new fits to multi-reference,
configuration interaction calculations, [5], scaled to reproduce
the barrier height and the experimental reaction exothermicity.
Fully-quantum, time-independent scattering calculations were done
by means of our extensively modified version [1] of the ABC
time-dependent, quantum reactive scattering code. [6] The lower the
energy, the longer the effective range of the potential, and the
more difficult the calculations.
[1] M. H. Alexander, D. E. Manolopoulos, and H. J. Werner, J. Chem. Phys. 113, 11084
(2000).
[2] L. Che, Z. Ren, X. Wang, W. Dong, et al., Science 317, 1061 (2007).
[3] F. Lique, M. H. Alexander, G. Li, H.-J. Werner, S. A. Nizkorodov, W. W. Harper, and D.
J. Nesbitt, J.
Chem. Phys. 128, 084313 (2008).
[4] E. Bodo, F. A. Gianturco, and A. Dalgarno, J. Phys. B 35, 2391 (2002); N. Balakrishnan
and A. Dalgarno,
Chem. Phys. Lett. 341, 652 (2001).
[5] G. Li, H.-J. Werner, F. Lique, and M. H. Alexander, J. Chem. Phys. 127, 174302
(2007).
[6] D. Skouteris, J. F. Castillo, and D. E. Manolopoulos, Comput. Phys. Comm. 133, 128
(2000).