Vacuum-UV spectroscopy of interstellar ice analogs. I. Absorption cross-sections of polar-ice molecules

Abstract

The VUV absorption cross sections of most molecular solids present in interstellar ice mantles with the exception of H2O, NH3, and CO2 have not been reported yet. Models of ice photoprocessing depend on the VUV absorption cross section of the ice to estimate the penetration depth and radiation dose, and in the past, gas phase cross section values were used as an approximation. We aim to estimate the VUV absorption cross section of molecular ice components. Pure ices composed of CO, H2O, CH3OH, NH3, or H2S were deposited at 8 K. The column density of the ice samples was measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. We provide VUV absorption cross sections of the reported molecular ices. Our results agree with those previously reported for H2O and NH3 ices. Vacuum-UV absorption cross section of CH3OH, CO, and H2S in solid phase are reported for the first time. H2S presents the highest absorption in the 120-160 nm range. Our method allows fast and readily available VUV spectroscopy of ices without the need to use a synchrotron beamline. We found that the ice absorption cross sections can be very different from the gas-phase values, and therefore, our data will significantly improve models that simulate the VUV photoprocessing and photodesorption of ice mantles. Photodesorption rates of pure ices, expressed in molecules per absorbed photon, can be derived from our data.

10 pages

References in corpus (1)

• The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects II: CO2

Cited by in corpus (26)

• Photochemistry and astrochemistry: photochemical pathways to interstellar complex organic molecules
• Modeling Sulfur Depletion in Interstellar Clouds
• First detection of interstellar S2H
• Impulsive Spot Heating and Thermal Explosion of Interstellar Grains Revisited
• Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules
• Methanol formation via oxygen insertion chemistry in ice
• Formation of Charon's Red Poles From Seasonally Cold-Trapped Volatiles
• A three-phase approach to grain surface chemistry in protoplanetary disks: Gas, ice surfaces and ice mantles of dust grains
• Bottlenecks to interstellar sulfur chemistry: Sulfur-bearing hydrides in UV-illuminated gas and grains
• Oxygen atom reactions with C2H6, C2H4, and C2H2 in ices
• New measurements on water ice photodesorption and product formation under ultraviolet irradiation
• Investigation of HNCO isomers formation in ice mantles by UV and thermal processing: an experimental approach
• UV photoprocessing of NH3 ice: photon-induced desorption mechanisms
• Vacuum ultraviolet photoabsorption spectroscopy of space-related ices: Formation and destruction of solid carbonic acid upon 1~keV electron irradiation
• Evolution of Morphological and Physical Properties of Laboratory Interstellar Organic Residues with Ultraviolet Irradiation
• Complex organic molecules in protoplanetary disks : X-ray photodesorption from methanol-containing ices. Part I -- Pure methanol ices
• Vacuum ultraviolet photoabsorption spectroscopy of space-related ices: 1 keV electron irradiation of nitrogen- and oxygen-rich ices
• Effects of $150-1000$ eV Electron Impacts on Pure Carbon Monoxide Ices using the Interstellar Energetic-Process System (IEPS)
• On The Photodesorption of CO${}_2$ Ice Analogues: The Formation of Atomic C in The Ice and the Effect of The VUV Emission Spectrume
• Ice mantles on dust grains: dramatic variation of thickness with grain size
• Vacuum ultraviolet photodesorption and photofragmentation of formaldehyde-containing ices
• ${}^{13}$CO and ${}^{13}$CO${}_2$ ice mixtures with N${}_2$ in photon energy transfer studies
• The formation of CO${}_2$ through consumption of gas-phase CO on vacuum-UV irradiated water ice
• 2-aminooxazole in astrophysical environments: IR spectra and destruction cross sections for energetic processing
• Synthesis of the first nitrogen-heterocycles in interstellar ice analogs containing methylamine (CH${}_3$NH${}_2$) exposed to UV radiation: Formation of trimethylentriamine (TMT, c-(-CH${}_2$-NH)${}_3$) and hexamethylentetramine (HMT, (CH${}_2$)${}_6$N${}_4$)
• Exploring refractory organics in extraterrestrial particles