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12 G. ROBERTS
Figure 1.5. Femtosecond spectroscopy of bimolecular collisions. The cartoon
shown in (a) illustrates how pump and probe pulses initiate and monitor the
progress of H CO →[HO . . . CO]→OH CO collisions. The build-up of OH
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product is recorded via the intensity of fluorescence excited by the probe laser as a
function of pump-probe time delay, as presented in (b). Potential energy curves
governing the collision between excited Na* atoms and H are given in (c); these
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show how the Na* H collision can proceed along two possible exit channels,
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leading either to formation of NaH H or to Na H by collisional energy
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exchange.