BEGIN:VCALENDAR VERSION:2.0 CALSCALE:GREGORIAN PRODID:UW-Physics-TWaP BEGIN:VEVENT SEQUENCE:0 UID:UW-Physics-Event-2241 DTSTART:20110930T203000Z DURATION:PT1H0M0S DTSTAMP:20191209T001156Z 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\, University of Wisconsin-Madison DESCRIPTION:Conical intersections between potential energy surfaces occur when the two electronic states become degenerate and\, consequently\, the Born-Oppenheimer approximation fails. Although long regarded as interesting curiosities\, it is now clear that they are central to a large variety of molecular transformations. Photodissociation and photoisomerization often occur by passage of electronically excited molecules through a conical intersection\, and the details of that passage control the partitioning of the products among competing pathways.


Similar studies in solution require 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 experiments an infrared pulse excites a vibration\, an ultraviolet pulse transfers molecules to an excited state\, and broadband continuum absorption monitors their evolution in the excited state. The competition between excited state vibrational relaxation and barrier crossing is the feature that determines the influence of vibrational excitation on the isomerization rate.