Excited state surface

Second-order effects include experiments designed to clock chemical reactions, pioneered by Zewail and coworkers [25]. The experiments are shown schematically in figure Al.6.10. An initial 100-150 fs pulse moves population from the bound ground state to the dissociative first excited state in ICN. A second pulse, time delayed from the first then moves population from the first excited state to the second excited state, which is also dissociative. By noting the frequency of light absorbed from tlie second pulse, Zewail can estimate the distance between the two excited-state surfaces and thus infer the motion of the initially prepared wavepacket on the first excited state (figure Al.6.10 ). 

Crim F F 1993 Vibrationally mediated photodissociation exploring excited state surfaces and controlling decomposition pathways Ann. Rev. Rhys. Chem. 44 397-428... 

IV. Interrogating Dynamics on Varying Regions of the Excited-State Surface... 

IV. INTERROGATING DYNAMICS ON VARYING REGIONS OF THE EXCITED-STATE SURFACE... 

An (avoided) crossing of So and Si need not even always correspond to a minimum in the excited state surface 64a>. Fig. 1 shows that this will depend on the slopes of the surfaces. Even such crossings which do not actually lead to a minimum in the excited state surface will be called funnels since they can provide efficient return to So- Further, if S2 lies very close to Si, vibronic coupling may make it impossible to describe the nuclear motion as specifically due to only one or the other hypersurface and both will have to be considered. Then, whether Si or S2 undergoes an avoided crossing with So may be immaterial — a funnel is still present and return of the molecule to So probable. 

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