Ammonia, carbon dioxide and the non-detection of the 2152 cm${}^{-1}$ CO band

Abstract

CO is one of the most abundant ice components on interstellar dust grains. When it is mixed with amorphous solid water (ASW) or located on its surface, an absorption band of CO at 2152 cm${}^{-1}$ is always present in laboratory measurements. This spectral feature is attributed to the interaction of CO with dangling-OH bonds (dOH) in ASW. However, this band is absent in observational spectra of interstellar ices. This raises the question whether CO forms a relatively pure layer on top of ASW or is in close contact with ASW, but not via dangling bonds. We aim to determine whether the incorporation of NH${}_3$ or CO${}_2$ into ASW blocks the dOH and therefore reduces the 2152 cm${}^{-1}$ band. We performed laboratory experiments to simulate the layered structure of the ice mantle, that is, we grew CO ice on top of 1) pure ASW, 2) NH${}_3$:H${}_2$O=10:100 mixed ice, and 3) CO${}_2$:H${}_2$O=20:100 mixed ice. Infrared spectra were measured to quantify the strength of the 2152 cm${}^{-1}$ band. In addition, a second set of experiments were performed to determine how the incorporation of NH${}_3$ into ASW affects the dOH band. We found that annealing the ice reduces the 2152 cm${}^{-1}$ band and that NH${}_3$ blocks the dOH on ASW surface and therefore reduces the 2152 cm${}^{-1}$ band more effectively than CO${}_2$. We suggest that this difference between NH${}_3$ and CO${}_2$ can be ascribed to the polarity of the guest molecule (NH${}_3$ is a polar species, whereas CO${}_2$ is apolar). The polarity implies that the formation of an H-bond between the N atom of ammonia and the dOH is a barrier-less reaction. We also determined the pore surface area of the ice mixtures as a function of the annealing temperature, and found that the nondetection of 2152 cm${}^{-1}$ band does not necessarily exclude the possibility of a porous ice mantle.

arXiv comment10 pages, 10 figures

References in corpus (33)

• Observations of the Icy Universe
• The Spitzer ice legacy: Ice evolution from cores to protostars
• The c2d Spitzer Spectroscopic Survey of Ices Around Low-Mass Young Stellar Objects: I. H2O and the 5-8 um Bands
• The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects II: CO2
• A 3-5 micron VLT spectroscopic survey of embedded young low mass stars I: Structure of the CO ice
• Mapping ices in protostellar environments on 1000 AU scales: Methanol-rich ice in the envelope of Serpens SMM 4
• The c2d Spitzer Spectroscopic Survey of Ices Around Low-Mass Young Stellar Objects. IV. NH3 and CH3OH
• Microscopic simulation of methanol and formaldehyde ice formation in cold dense cores
• Disk Imaging Survey of Chemistry with SMA (DISCS): I. Taurus Protoplanetary Disk Data
• Ice and Dust in the Quiescent Medium of Isolated Dense Cores
• Binding energies of interstellar molecules on crystalline and amorphous models of water ice by ab-initio calculations
• CO2 formation in quiescent clouds; an experimental study of the CO + OH pathway
• An experimental study of the surface formation of methane in interstellar molecular clouds
• Binding Energy of Molecules on Water Ice: Laboratory Measurements and Modeling
• First Detection of Near-Infrared Line Emission from Organics in Young Circumstellar Disks
• CO diffusion into amorphous H2O ices
• First detection of gas-phase ammonia in a planet-forming disk
• The Environment and Nature of the Class I Protostar Elias 29: Molecular Gas Observations and the Location of Ices
• CO2 infrared emission as a diagnostic of planet-forming regions of disks
• Changes in the morphology of interstellar ice analogues after hydrogen atom exposure
• Measurements of diffusion of volatiles in amorphous solid water: application to interstellar medium environments
• A survey of H${}_2$O, CO${}_2$ and CO ice features towards background stars and low mass YSOs using AKARI
• IR Spectral Fingerprint of Carbon Monoxide in Interstellar Water Ice Models
• Linking ice and gas in the Serpens low-mass star-forming region
• Diffusion and Clustering of Carbon Dioxide on non-porous Amorphous Solid Water
• Observations of the Onset of Complex Organic Molecule Formation in Interstellar Ices
• The nitrogen carrier in protoplanetary disks
• The ${}^{12}$CO${}_2$ and ${}^{13}$CO${}_2$ Absorption Bands as Tracers of the Thermal History of Interstellar Icy Grain Mantles
• Bright CO ro-vibrational emission lines in the class I source GSS 30 IRS1: Probing the inner disk of a young embedded star
• Water and Methanol Ice in L1544
• The Effective Surface Area of Amorphous Solid Water Measured by the Infrared Absorption of Carbon Monoxide
• High-Resolution Mid-Infrared Spectroscopy of GV Tau N: Surface Accretion and Detection of Ammonia in a Young Protoplanetary Disk
• Linking ice and gas in the Lambda Orionis Barnard 35A cloud

Cited by in corpus (1)

• Infrared band strengths of dangling OH features in amorphous water at 20 K