A theoretical study of I2 vibrational motion after excitation with an ultrashort pulse

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Abstract
We calculate the population created by a short pump pulse exciting the I2 molecule to the bound region of the B state, followed by excitation with a short probe pulse to the state E (or F). The nuclear state produced by the pump oscillates in the well of the B state and the probe is absorbed to populate the E (or F) state only when the wave function passes through the Franck–Condon region of the B→E (or B→F) transition. Because of this, the population on the E (or F) state oscillates with the delay time between the pump and the probe. The calculations agree with the experiment in the case when the probe excites the E state. When the F state is excited the theory predicts a doublet structure which is not observed; moreover, in some cases the experiment and theory differ at the shortest delay times. We discuss the dependence of the LIF signal on the pulse width and the initial state, the long time behavior of the LIF signal, and illustrate the role of the population transients on the B states at early times, during or immediately after the pump pulse acted on the molecule.