The effective delay time in pump-and-probe measurements

The delay time for secondary collisions is considered for systems in which a reactant is created by one short laser pulse, and a product detected with a second short laser pulse at some later time. Sample calculations for the Mg(1P1)+H2→ MgH+H reaction show that the average (or ‘‘effective’’) delay time for secondary collisions of MgH product is different from and not necessarily linearly related to the delay time between the two laser pulses.