Synthesis of gaseous and solid organics by photon ionization/dissociation of gas mixtures in a VUV cell coupled to the DESIRS line at Soleil synchrotron
We shall illuminate gas mixtures of H2-CO-CH4-N2-noble gas compositions with VUV photons. We want to investigate (i) noble gas isotope fractionation upon photon ionization, (ii) IF and MIF of H, C, N and O in run products, and (iii) the nature of isotope fractionation, that is, self-shielding or pre-dissociation mixing. We shall use a VUV photochemical cell named APSIS (for Atmospheric Photochemistry SImulated by Synchrotron) already developed in the LATMOS laboratory (collaboration, N. Carrasco) that will be coupled to the DESIRS beamline on the SOLEIL synchrotron.
For photons below 140 nm, a windowless system is required because the synchrotron light is absorbed by all materials. This constraint requires the development of a differential pumping unit in which the mbar pressure range has to decrease to the 10-8 mbar range in the downstream part of the beamline. The APSIS VUV photochemical cell is a on-site gas flow system with differential pumping and product cryogenic trapping capability, with on-site dynamic mass spectrometry. Only one other VUV atmospheric photoreactor exists, which is coupled to a VUV synchrotron beamline in Berkeley (Imanaka and Smith 2010).
DESIRS (Dichroïsme Et Spectroscopie par Interaction avec le Rayonnement Synchrotron) line at the Soleil Synchrotron (St Aubin, F)) is an undulator-based beamline covering the FUV range (5-40 eV; 30-250 nm). The average density can be tailored between 1013 and 1019 ph.sec-1.cm-2. This high flux is delivered at typically 100’s of MHz repetition rate, ie in a quasi-continuous mode, preventing non-linear absorption processes. The figure shows a scheme of the beamline and in particular the free port (branch B) on which the present proposal set-up will be connected. Flux curve for different resolving power (in the first order mode) are also shown.