Photodesorption of Acetonitrile CH₃CN in UV-irradiated Regions of the Interstellar Medium: Experimental Evidence

Pure acetonitrile (CH3CN) and mixed CO:CH3CN H2O:CH3CN ices have been irradiated at 15K with Vacuum UltraViolet (VUV) photons in the 7-13.6 eV range using synchrotron radiation. VUV photodesorption yields of CH3CN photo-products derived as a function incident photon energy. The coadsorption CO H2O molecules, which are expected to be among main constituents interstellar ices, is found no significant influence on spectra CH3CN, CHCN, HCN, CN CH3. Contrary what has generally evidenced for most condensed these findings point toward desorption process molecule that absorbs one desorbing. It can ejected gas phase intact or form its photo-dissociation fragments. Astrophysical yields, applicable different locations, incorporated into astrochemical modeling. They vary from 0.67(+/-0.33).10^{-5} 2.0(+/-1.0).10^{-5} molecule/photon depending region considered, high compared other organic molecules such methanol. These results could explain multiple detections regions medium well-correlated astrophysical observations Horsehead nebula protoplanetary disks (such TW Hya HD 163296).