Channel-selective analysis of strong-field-induced nuclear wave packet in sulfur dioxide*

The temporal evolution of vibrational wave packets in sulfur dioxide molecules irradiated by intense 800 nm laser pulses is studied employing momentum-resolved ion spectroscopy and channel-selective Fourier analysis. We map the wave-packet dynamics created by laser ionization or excitation of the molecule using two different probe schemes: weak-field excitation by a 300 nm laser pulse and strong-field excitation or ionization by a second 800 nm pulse. The 300 nm pulse exclusively probes bending vibrations in the ground state of the SO₂⁺ ion by a one-photon resonant coupling to a single repulsive excited state. In contrast, the 800 nm probe pulse can map the dynamics via a broad range of singly, doubly or multiply charged final states, either bound or dissociative. While the signal in all channels is dominated by the ionic-state bending vibrations, the Fourier analysis of delay-dependent ion yields also reveals the signatures of the same vibrational mode in the ground state of the neutral SO₂ molecule. We discuss how the choice of the final state populated by the probe pulse influences the Fourier spectra and the phase of the observed oscillations, and compare the experimental results to the predictions of the theoretical model simulating the wave packet propagation in SO₂ neutral and ionic ground states.