  Ionization of acetylene by linearly-polarized, vacuum ultraviolet (VUV) laser
pulses is modelled using time-dependent density functional theory. Several
laser wavelengths are considered including one that produces direct ionization
to the first excited cationic state while another excites the molecules to a
Rydberg series incorporating an autoionizing state. We show that for the
wavelengths and intensities considered, ionization is greatest whenever the
molecule is aligned along the laser polarization direction. By considering high
harmonic generation we show that populating excited states can lead to a large
enhancement in the harmonic yield. Lastly, angularly-resolved photoelectron
spectra are calculated which show how the energy profile of the emitted
electrons significantly changes in the presence of these excited states.
