BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-2241
DTSTART:20110930T203000Z
DURATION:PT1H0M0S
DTSTAMP:20260419T063816Z
LAST-MODIFIED:20110923T133924Z
LOCATION:2241 Chamberlin Hall (coffee at 4:30 pm)
SUMMARY:Vibrations\, Conical Intersections\, and Reaction Dynamics in 
 Gases and Liquids\, Physics Department Colloquium\, Fleming Crim\, Uni
 versity of Wisconsin-Madison
DESCRIPTION:Conical intersections between potential energy surfaces oc
 cur when the two electronic states become degenerate and\, consequentl
 y\, the Born-Oppenheimer approximation fails. Although long regarded a
 s interesting curiosities\, it is now clear that they are central to a
  large variety of molecular transformations. Photodissociation and pho
 toisomerization often occur by passage of electronically excited molec
 ules through a conical intersection\, and the details of that passage 
 control the partitioning of the products among competing pathways.<br>
 
\n<br>
\nAmmonia is a prototypical molecule in which a conical inters
 ection is important in excited-state dissociation. High resolution stu
 dies of the dissociation of isolated ammonia molecules show that excit
 ation of selected vibrations changes the course of the dissociation dr
 amatically\, leading to the formation of electronically excited produc
 ts at the expense of ground-state products. The key to this behavior i
 s the influence of vibrational motion on passage of the system through
  the conical intersection. <br>
\n<br>
\nSimilar studies in solution r
 equire high time resolution rather than high spectral resolution\, and
  it is possible to prepare vibrationally excited molecules in solution
  and monitor their evolution using 100-fs laser pulses. In these exper
 iments an infrared pulse excites a vibration\, an ultraviolet pulse tr
 ansfers molecules to an excited state\, and broadband continuum absorp
 tion monitors their evolution in the excited state. The competition be
 tween excited state vibrational relaxation and barrier crossing is the
  feature that determines the influence of vibrational excitation on th
 e isomerization rate.<br>
\n
URL:https://www.physics.wisc.edu/events/?id=2241
END:VEVENT
END:VCALENDAR