Work

IR-Induced CO Photodesorption from Pure CO Ice and CO on Amorphous Solid Water

Year: 2025

Type: article

Abstract: O ice. This CO plays an important role in the formation of complex organic molecules (COMs) through reactions with hydrogen atoms. Interstellar grains are also exposed to photons and charged particles that can both drive chemical reactions and promote desorption of molecules, providing an important link between the solid state reservoir of molecules and the gas phase. While several studies have considered UV photon driven desorption mechanisms, the UV component of the interstellar radiation field is strongly attenuated within dense clouds, with the internal cloud field being dominated by IR photons. We have used the FELIX IR Free Electron Laser (FEL) FEL-2 to irradiate a few monolayer film of CO deposited on the top of amorphous solid water (ASW) and compared the CO desorption yields to those obtained for a pure CO film. Infrared spectroscopy, combined with mass spectrometric detection of desorbing CO molecules, reveals that excitation of vibrational modes in the underlying ASW leads to significant CO desorption. This is in contrast to direct excitation of the stretching mode of CO which results in only inefficient desorption. The desorption efficiencies we derive indicate that energy transfer within ices on interstellar grains might provide an important route to IR photon-induced desorption of volatile species, such as CO.

Source: ACS Earth and Space Chemistry

DOI: 10.1021/acsearthspacechem.5c00040