Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ammonia in water-dominated ice mixtures explains the non-detection of
  the 2152 cm$^{-1}$ band   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 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 performed laboratory experiments to simulate the layered structure of
the ice mantle, i.e., 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. 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 non-detection of 2152 cm$^{-1}$
band does not necessarily exclude the possibility of a porous ice mantle.

2
The categories of this paper are: math
18
The categories of this paper are: econ
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
29
The categories of this paper are: funct-an
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex