Vibrational wave packets in the C 1Πu state of Cs2: Two color pump–probe experiments

Two color, pump–probe laser experiments on the ∼100 fs time scale have been applied to examining the dynamics of vibrational wave packets in the C 1Πu state of Cs2. Wave packets consisting of more than 20 C state vibrational levels are produced with an initial pulse having a central wavelength between ∼620 and 680 nm. The temporal history of the wave packet is inferred from the time and energy-integrated photoelectron signal produced when the excited state is photoionized by a time-delayed pulse centered at 605, 610, 615, 617, or 620 nm. Because of the difference in equilibrium internuclear separations for the Cs2(C) and Cs+2(X) states (ΔRe≊0.75 Å), wave packets are readily observed (signal-to-noise ratio ≳10) without the need to resort to mass selection techniques. Frequency analysis of the wave packet data shows a dominant (fundamental) component that decreases from 29 to ∼28.3 cm−1 as the pump wavelength is tuned from 627 to 641 nm. Other spectral modes at ∼23.5 and ∼34 cm−1 and a weaker term at twice the fundamental frequency are also observed and quantum mechanical calculations of the wavepacket motion are in accord with the experimental results.