With our new paper, "CO desorption from interstellar icy grains induced by infrared excitation of superhydrogenated polycyclic aromatic hydrocarbons", we continue to examine this question.

In dense, interstellar clouds, dust grains are covered in icy mantles where CO is a key component. The icy grains are constantly exposed to radiation, dominated by infrared (IR) photons within dense clouds. In this work, we used the FELIX Free Electron Laser in Nijmegen, the Netherlands, to examine the effect of such IR radiation on CO ices, mixed and layered with perhydropyrene (PHP). PHP is a superhydrogenated polycyclic aromatic hydrocarbon representing large carbonaceous molecules and hydrogenated carbonaceous grains present in the interstellar medium.

Our work demonstrates that the vibrational excitation of the PHP CH stretching modes leads to significant CO desorption for both systems. This indicates that IR excitation of carbonaceous molecules and grains in dense clouds could play an important role in the desorption of volatile species such as CO from icy grains. This is in accordance with our previous work, showing that excitation of vibrational modes in H2O ice can similarly lead to CO desorption, indicating that IR-induced desorption processes in general could provide a crucial link between the ice and gas in interstellar clouds.

Read the new paper here: https://www.aanda.org/articles/aa/full_html/2025/12/aa56399-25/aa56399-25.html