WAVEPACKET CALCULATIONS OF FEMTOSECOND PUMP-PROBE EXPERIMENTS ON THE SODIUM TRIMER

Wavepacket calculations are carried out to simulate femtosecond pump-p robe experiments involving pseudorotational motion on the B state of t he sodium trimer. The calculations are carried out in two dimensions, corresponding to the radical and angular pseudorotation modes. Simple potential energy surfaces appropriate for second-order Jahn-Teller and pseudo-Jahn-Teller effects are used. The initial wavepacket on the B state is created by explicit modeling of the short-pulse excitation pr ocess, taking proper account of interference effects that occur on the B-state surface. The resulting wavepacket is propagated for up to 20 ps by using the Chebyshev propagator. The ionization signal is then si mulated in three different ways: (i) explicit modeling of the probe la ser; (ii) overlap between the wavepacket on the B state and the ground -state ion wavefunction; (iii) the zero-time autocorrelation function on the B state. The ionic overlap method is found to be in fair agreem ent with the exact method, but the zero-time autocorrelation function is not. The results show reasonable agreement with the frequencies obt ained from the experimental work; but the intensities do not agree wel l.