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Abstract:
The acetylene-vinylidene system serves as a benchmark for investigations
of ultrafast dynamical processes where the coupling of the electronic
and nuclear degrees of freedom provides a fertile playground to explore
the femto- and sub-femto-second physics with coherent
extreme-ultraviolet (EUV) photon sources both on the table-top as well
as free-electron lasers. We focus on detailed investigations of this
molecular system in the photon energy range 19-40 eV where EUV pulses
can probe the dynamics effectively. We employ photoelectron-photoion
coincidence (PEPICO) spectroscopy to uncover hitherto unrevealed aspects
of this system. In this work, the role of excited states of the C2H2+
cation, the primary photoion, is specifically addressed. From
photoelectron energy spectra and angular distributions, the nature of
the dissociation and isomerization channels is discerned. Exploiting the
4 pi -collection geometry of the velocity map imaging spectrometer, we
not only probe pathways where the efficiency of photoionization is
inherently high but also perform PEPICO spectroscopy on relatively weak
channels.
