The multielectron ionization dynamics underlying attosecond strong field spectroscopies

Sub-cycle strong field ionization (SFI) underlies many emerging spectroscopic probes
of atomic or molecular attosecond electronic dynamics. Extending methods such
as attosecond high harmonic generation (HHG) spectroscopy to complex polyatomic
molecules requires an understanding of multielectronic excitations, already hinted at
by theoretical modelling of experiments on atoms, diatomics, and triatomics. Here we
present a direct method which, independent of theory, experimentally probes the par-
ticipation of multiple electronic continua in the SFI dynamics of polyatomic molecules.
We show, using saturated (C4H10) and unsaturated (C4H6) linear hydrocarbons, how
sub-cycle SFI of polyatomics can be directly resolved into its distinct electronic contin-
uum channels by above threshold ionization photoelectron spectroscopy. Our approach
makes use of photoelectron-photofragment coincidences, suiting broad classes of poly-
atomic molecules.