Cryogenic Chemistry and Quantitative Non-Thermal Desorption from Pure Methanol Ices: High-Energy Electron versus X-Ray Induced Processes

X-Ray irradiation of interstellar ice analogues has recently been proven to induce desorption of molecules, thus being a potential source for the still-unexplained presence of gaseous organics in the coldest regions of the interstellar medium, especially in protoplanetary disks. The proposed desorption mechanism involves the Auger decay of excited molecules following soft X-ray absorption, known as X-ray induced electron-stimulated desorption (XESD). Aiming to quantify electron induced desorption in XESD, we irradiated pure methanol (CH3OH) ices at 23 K with 505 eV electrons, to simulate the Auger electrons originating from the O 1s core absorption. Desorption yields of neutral fragments and the effective methanol depletion cross-section were quantitatively determined by mass spectrometry. We derived desorption yields in molecules per incident electron for CO, CO2, CH3OH, CH4/O, H2O, H2CO, C2H6 and other less abundant but more complex organic products. We obtained desorption yields remarkably similar to XESD values.

Automated summary

Recent research has found that X-ray irradiation of interstellar ice analogues can induce molecule desorption, potentially explaining the presence of gaseous organics in the coldest regions of the interstellar medium, particularly in protoplanetary disks. The proposed desorption mechanism involves the Auger decay of excited molecules following soft X-ray absorption, known as X-ray induced electron-stimulated desorption (XESD). In this study, pure methanol (CH3OH) ices were irradiated with 505 eV electrons to simulate the Auger electrons, and desorption yields of various organic fragments were quantitatively determined by mass spectrometry, showing remarkable similarity to XESD values.