Ice analogs database
This database contains the infrared spectra (4000 -- 400 cm-1) of laboratory
analogs of interstellar ices. These analogs consist of mixtures of
the molecules H2, H2O, NH3, CH4, CO, H2CO, CH3OH, O2, N2, and CO2.
These mixtures can contain from 1 up to 3 of these components.
For each sample spectra are available for a number of systematically
increasing UV doses, and at a number of different temperatures.
The data is supplied as simple text files with 2 columns. The units are
cm-1 and Absorbance (=(Optical depth)/ln10).
A detailed description of the experimental procedures can be found in
Gerakines et al. 1995 (Astronomy and Astrophysics 296, 810) and
Gerakines et al. 1996. Only the directly relevant features are described here.
Ice samples consisting of a mixture of gases are deposited on a CsI window
inside a vacuum chamber at a temperature of 10 K. Subsequent irradiation is
performed with a hydrogen discharge vacuum UV lamp which gives a nominal flux
of 1.0E+15 photons cm-2 s-1 (Ephoton > 6 eV), with an uncertainty of about a
factor 2. Irradiation doses are stepwise increased, and generally correspond
to 5s, 15s, 1m, 3m, 10m or 12m, and 1h irradiation time. After the final
irradiation step, gradual warm-up was performed, generally to 50, 80, 120, 160
K. In most cases also higher temperatures were studied, but not at standard
values. A spectrum is obtained just before sample deposition (the background),
and then at each of the above defined experimental stages. The final spectrum
is made by ratioing the spectrum by the background.
The thickness of the samples were choosen at 0.11-0.15 micron. This choice
optimizes S/N on the obtained features, while still ensuring (near) optical
thinness (~ 50 % of the UV radiation is absorbed by the sample).
Resolution equals 1 cm-1 for the experiments involving pure compounds,
and 2 cm-1 for the mixtures.
Summary of experiments
The table below summarizes the samples for which measurements have been
performed. The first column gives the name of the experiment. The name
was constructed as comp1[_comp2[_comp3]_number], where comp1, comp2 and
comp3 are the molecular constituents, while, in case of 2 components,
the number gives the abundance of component 2 relative to 1, or, for
three components it is just a numerical identifier of this particular
Experiment Composition Date Ori.Name Comment
comp.1 comp.2 comp.3 comp.4
H2O 100 080295 PE15
NH3 100 100295 PE17
CH4 100 160295 PE21
CO 100 260195 PE07
CO2 100 010295 PE10
H2CO 100 240195 PE06
CH3OH 100 030395 PE25 10K spectra
100 060395 PE26 > 10K
O2 100 030295 PE12
N2 100 060295 PE13
H2O_NH3_20 100 20 251295 B08
H2O_CH4_33 100 33 010196 B10
H2O_CO_33 100 33 141195 B05
H2O_O2_20 100 20 251295 B07
H2O_CH3OH_100 100 100 071195 B03
NH3_CH3OH_50 100 50 091195 B04
NH3_O2_100 100 100 290296 B17
CO_H2O_10 100 10 161195 B06
CO_NH3_100 100 100 240296 B15
CO_O2_100 100 100 120196 B12
O2_H2O_10 100 10 110196 B11
O2_N2_100 100 100 250296 B16
H2O_CO_H2_1 100 33 33 020296 B14 Sticking H2 < 100%
H2O_CO_NH3_1 100 23 21 XCN10
A few isolated spurious features result from a few limitations in the
procedure. First, due to the use of a sandwich of frozen layers of Ar
to embed the actual sample (see Gerakines et al. 1996 for a description
of this technique), lines are introduced of H2O molecules diluted in Ar
caused by the presence of residual traces of water in the vacuum set-up.
These lines can be found between 1580 and 1670 cm-1 and are often visible
after 3m of irradiation (At earlier stages they can be corrected).
Second, a number of sharp features appear during warm-up, for example at 1095
and 1235 cm-1.
These features are due to the presence of some organic material absorbed
on the CsI substrate. Normally the corresponding features are fully
eliminated when the ratioing by the background takes place. However,
the features are sometimes temperature dependent causing the presence of
the sharp structure in the warm-up spectra.
Finally a sharp strong peak is usually found at ~700 cm-1 which is related
to the vibration of the set-up caused by the cryogenic system.
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Last modified: Mon Jan 8 13:33:52 GMT 1996