J/A+A/629/A112 Complex refractive index of CO ice (Giuliano+, 2019)
Broadband spectroscopy of astrophysical ice analogues.
I. Direct measurement of complex refractive index of CO ice using terahertz
time-domain spectroscopy.
Giuliano B.M., Gavdush A.A., Mueller B., Zaytsev K.I., Grassi T.,
Ivlev A.V., Palumbo M.E., Baratta G.A., Scire C., Komandin G.A.,
Yurchenko S.O., Caselli P.
<Astron. Astrophys. 629, A112 (2019)>
=2019A&A...629A.112G 2019A&A...629A.112G (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Carbon monoxide ; Spectroscopy
Keywords: astrochemistry - methods: laboratory: solid state - ISM: molecules -
infrared: ISM
Abstract:
Reliable, directly measured optical properties of astrophysical ice
analogs in the infrared (IR) and terahertz (THz) range are missing.
These parameters are of great importance to model the dust continuum
radiative transfer in dense and cold regions, where thick ice mantles
are present, and are necessary for the interpretation of future
observations planned in the far-IR region.
Coherent THz radiation allows direct measurement of the complex
dielectric function (refractive index) of astrophysically relevant ice
species in the THz range.
The time-domain waveforms and the frequency-domain spectra of
reference samples of CO ice, deposited at a temperature of 28.5K and
annealed to 33K at different thicknesses, have been recorded. A new
algorithm is developed to reconstruct the real and imaginary parts of
the refractive index from the time-domain THz data.
The complex refractive index in the wavelength range of 1mm-150um
(0.3-2.0THz) has been determined for the studied ice samples, and
compared with available data found in the literature.
The developed algorithm of reconstructing the real and imaginary parts
of the refractive index from the time-domain THz data enables, for the
first time, the determination of optical properties of astrophysical
ice analogs without using the Kramers-Kronig relations. The obtained
data provide a benchmark to interpret the observational data from
current ground based facilities as well as future space telescope
missions, and have been used to estimate the opacities of the dust
grains in presence of CO ice mantles.
Description:
Optical properties of CO ice. (a) Real part of the refractive index,
(b) amplitude absorption coefficient, (c) real and (d) imaginary parts
of the dielectric permittivity (see Eqs. 1 and 2). For all deposition
intervals, the dielectric curves demonstrate the existence of a
Lorenz-like absorption peak, centered near 1.5THz and featuring
similar bandwidth. Distortions of the results seen at frequencies
below 0.3THz (such as an oscillatory character of n and varepsilon as
well as an increase of varepsilon with decreasing frequency) are due
to diffraction effects (see Sec.2.2).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig6_4m.dat 75 135 Complex refractive index and dielectric
properties for 4 min steps deposition
fig6_5m.dat 75 135 Complex refractive index and dielectric
properties for 5 min steps deposition
fig6_6m.dat 75 135 Complex refractive index and dielectric
properties for 6 min steps deposition
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Byte-by-byte Description of file (#): fig6_4m.dat fig6_5m.dat fig6_6m.dat
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Bytes Format Units Label Explanations
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1- 11 F11.9 THz Freq Frequency
17- 27 F11.9 --- nre Real refractive index
32- 43 F12.9 --- alpha Amplitude absorption coefficient
49- 59 F11.9 --- eps-real Real dielectric permittivity
65- 75 F11.9 --- eps-imag Imaginary dielectric permittivity
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Acknowledgements:
Barbara Michela Giuliano, giuliano(at)mpe.mpg.de
(End) Patricia Vannier [CDS] 26-Jul-2019