Flux and fluence effects on the Vacuum-UV photodesorption and photoprocessing of CO${}_2$ ices

Abstract

CO${}_2$ is a major component of the icy mantles surrounding dust grains in planet and star formation regions. Understanding its photodesorption is crucial for explaining gas phase abundances in the coldest environments of the interstellar medium irradiated by vacuum-UV (VUV) photons. Photodesorption yields determined experimentally from CO${}_2$ samples grown at low temperatures (T=15~K) have been found to be very sensitive to experimental methods and conditions. Several mechanisms have been suggested for explaining the desorption of CO${}_2$, O${}_2$ and CO from CO${}_2$ ices. In the present study, the cross sections characterizing the dynamics of photodesorption as a function of photon fluence (determined from released molecules in the gas phase) and of ice composition modification (determined in situ in the solid phase) are compared for the first time for different photon flux conditions (from 7.3$\times 10^{12}$~photon/s/cm${}^2$ to 2.2$\times 10^{14}$~photon/s/cm${}^2$) using monochromatic synchrotron radiation in the VUV range (on the DESIRS beamline at SOLEIL). This approach reveals that CO and O${}_2$ desorption are decorrelated from that of CO${}_2$. CO and O${}_2$ photodesorption yields depend on photon flux conditions and can be linked to surface chemistry. By contrast, the phodesorption yield of CO${}_2$ is independent of the photon flux conditions and can be linked to bulk ice chemical modification, consistently with an indirect desorption induced by electronic transition (DIET) process.

arXiv comment11 pages, 7 figures

References in corpus (15)

• Observations of the Icy Universe
• An Ice Age JWST inventory of dense molecular cloud ices
• Detection of the Water Reservoir in a Forming Planetary System
• The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects II: CO2
• Photodesorption of ices I: CO, N2 and CO2
• Dust as interstellar catalyst I. Quantifying the chemical desorption process
• CO ice photodesorption: A wavelength-dependent study
• Indirect ultraviolet photodesorption from CO:N2 binary ices - an efficient grain-gas process
• CEERS Key Paper VI: JWST/MIRI Uncovers a Large Population of Obscured AGN at High Redshifts
• The IRAM-30m line survey of the Horsehead PDR: IV. Comparative chemistry of H2CO and CH3OH
• Gas-phase H2O and CO2 toward massive protostars
• Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules
• CO${}_2$ Infrared Phonon Modes in Interstellar Ice Mixtures
• On The Photodesorption of CO${}_2$ Ice Analogues: The Formation of Atomic C in The Ice and the Effect of The VUV Emission Spectrume
• Mechanism of Indirect Photon-induced Desorption at the Water Ice Surface