[MOS] November 21, 2007

[Zina Queen]

Seminar on
Modern Optics and Spectroscopy


Hans Bechtel, MIT

Partner swapping:  Another reason to pump and dump

November 21, 2006

12:00 noon - 1:00 p.m.
Grier Room 34-401



Abstract:

Isomerization reactions, in which a molecule 
keeps the same set of atoms, but swaps partners, 
are prevalent in all areas of chemistry and have 
strong implications for astronomy, biology, 
combustion, and the environment.  We study 
prototypical isomerization reactions with high 
energy barriers such as HCN î HNC, HCCH î CCH2, 
and NCCN î NCNC.  In order to better elucidate 
the nature of these reactions, we wish to observe 
molecules in states of undress, i.e. near the top 
of the energy barrier while old bonds are being 
broken and new bonds are being formed.  These 
barrier proximal states are hard to identify 
because they are only a small subset of the more 
numerous and less interesting highly excited 
vibrational states.  The large amplitude motion 
embodied in the rare barrier-proximal states, 
however, causes changes in the electronic 
properties of the molecule that provide markers 
to distinguish them from other states.  To 
prepare these highly energetic states with 
non-equilibrium motions, we rely on stimulated 
emission pumping (SEP), a double resonance 
technique involving a PUMP laser to an excited 
electronic state and a DUMP laser back to the 
ground electronic potential energy surface.
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