Add to ORKGInternational audienceWe report here a new reactor, named APSIS for Atmospheric Photochemistry SImulated by Synchrotron, where a gas mixture (N2/CH4=90/10) at various pressures in the mbar range in the reactor is irradiated using the continuous-spectrum (60-350 nm) DISCO beam in the SOLEIL Radiation Facility. The photochemical products, in situ detected by quadrupole mass spectrometry, include C2, C3, C4 and probably C5 compounds.We compared the neutral productions in APSIS and other experiments with the INMS measurements