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.


Boguslavskiy, A. E., Mikosch, J., Gijsbertsen, A., Spanner, M., Patchkovski, S., Gador, N., … Stolow, A. (2012). The multielectron ionization dynamics underlying attosecond strong field spectroscopies. Science, 335(6074), 1336–1340. doi:10.1126/science.1212896