Pulse train induced dynamics

Starting from the groimd vibrational state on the ground (X) electronic state, we form a wavepacket on the first excited (A) state with a 2-axis polarized prnnp pulse of the form of Eq. (3.84) with intensity = 4 X 10 W cm, tvjjz = 3.63 eV, and a Gaussian envelope of FWHM r, = 8 fs. 

The pump pulse causes 74% excitation into the A state (between t = —8 and 4 fs). Afterwards the probe pulse train causes transfer of population between the A and B states, and between B and C (and X) states. Transfer of population occurs synchronous with the pulses in the pulse train, causing the step-like appearance seen in Fig. 5.35(a). The pulse train causes ionization simultaneously with population transfer among the neutral states. Time evolution of the ionized population is also seen to be step-like, with change synchronous with the pulses. Thus the electronic excitation and deexcitation seems to be a Rabi oscillation whose timing of transition is well controlled. On the other hand, the relevant nuclear vibrational motion is autonomously evolved in time during the refractory period. 

The transition from the B state to the X state takes place at a tmning point of the latter, where a large value of the Franck-Condon overlap is expected. On the other hand, major transitions in B — A and B — C are realized in the regions where the involved potential functions are geometrically flat, in the range of 1.5-3.5 A for the A state, 2.0 A and larger for the 

Chemical Theory Beyond the Born-Oppenheimer Paradigm 

B state, and 1.8-2.5 A for the C state. In these ranges, electronic transition takes place as though it makes a copy of vibrational wavefunction in the common regions between the relevant electronic states. This is a reflection of the Condon principle. We note that there is counter-intuitive decrease of population in the potential well of the X state when omitting ionization, especially in the panels for Pulse 2 and Pulse 6, indicating there is some deexcitation from the excited electronic states via Rabi-oscillation like coupling with the ion continuum. Thus, complicated transfer, overlapping, and dispersion of the vibrational wavepackets proceed in each electronic state in a stepwise manner. Very fine information in the attosecond time scale is thus folded in the complicated structures and phases of the set of vibrational wavepackets [305]. 

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