Multidimensional electron-nuclear wavepacket dynamics via Time-, Energy- and Angle-resolved Photoelectron Spectroscopy.

Generating and probing a coherent superposition of coupled vibrational-electronic (vibronic) states -- a multidimensional wavepacket -- remains a challenging problem in molecular dynamics. Here, we present recent results using time-resolved photoelectron velocity map imaging (VMI) of complex vibronic wavepacket dynamics in the NO molecule following femtosecond single photon excitation in the vacuum ultraviolet (VUV) range ($\lambda_{\mathrm{pump}}=$ 160 nm, 80 fs). The induced ultrafast dynamics, involving highly excited valence and Rydberg states, is probed by single photon ionization ($\lambda_{\mathrm{probe}}=$ 400 nm, 40 fs). Varying the pump-probe time delay, the emitted photoelectrons are detected in a VMI spectrometer for time-, energy- and angle-resolved photoelectron spectroscopy. We observe that the different final vibrational states of the NO$^{\mathrm{+}}$ (X $^{\mathrm{1}}\Sigma^{\mathrm{+}})$ cation, onto which this evolving vibronic wavepacket is projected, reveal different time dependences for the kinetic energy distribution and the laboratory frame photoelectron angular distribution (LFPAD). In particular, we observe unusually strong oscillations in the $\beta_{\mathrm{4}}$ asymmetry parameter, indicating sensitivity to the higher angular momentum components of the electronic aspect of this complex vibronic wavepacket.