Astrochemistry Laboratory
Optical Constants from IR Spectra - The Cosmic Ice Laboratory - Sciences and Exploration Directorate - NASA's Goddard Space Flight Center

The Cosmic Ice Laboratory - IR Spectra

The Cosmic Ice Laboratory - Optical Constants from IR Spectra




Optical Constants - Free Software

Astrochemists and others have been calculating optical constants (n and k) for decades, but there seems to be no free and open-source software for such work. The program we wrote (almost entirely the work of Perry Gerakines) is described in a paper in The Astrophysical Journal (Gerakines & Hudson, 2020). A copy of the software is here, as a "zipped" file. It's free, fast, accurate, open-source, easy-to-use, and available in both a Python and a Windows-executable version.

If you find this program helpful in your research then please acknowledge any use by reference to "Gerakines & Hudson, 2020" and this NASA web site. Variations of this work come to mind, and so we would be glad to have copies of any improvements you make.

Interference Fringes - Free Software

This Excel file (394 kilobytes) will allow you to fit a set of interference fringes with a method similar to that described by Romanescu et al. (Icarus, 2010). The calculation is not particularly difficult, but we are unaware of a free, open-source computer routine for doing it, and that employs a straightforward graphical user interface. We have tested the file given here and know that it works with Excel and the OpenOffice package. Note that there are instructions in the second and third tabs at the bottom of the spreadsheet.

If you find this file helpful in your research then please acknowledge any use by reference to "Hudson et al." and this NASA web site. Variations of this work come to mind, and so we would be glad to have copies of any improvements you make.

Spectral Calculation - Free Software

This Excel file (4.76 megabytes) will allow you to calculate IR transmission spectra from optical constants, n and k, based on the method of Swanepoel (1983) referenced in the file. The calculation is not particularly difficult, but we are unaware of a free, open-source computer routine for doing it, and using a straightforward graphical user interface. We have tested the file given here and know that it works with Excel and the OpenOffice package.

If you find this file helpful in your research then please acknowledge any use by reference to "Hudson et al." and this NASA web site. Many variations of this file come to mind, and so we would be glad to have copies of any improvements you make.

Carbon Monoxide

This Excel file (1.37 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of alpha-crystalline CO (carbon monoxide) at 25 K at resolutions of 0.5 and 1 cm-1. A full description is in Gerakines, Materese, and Hudson, Monthly Notices of the Royal Astronomical Society, 2023 (accepted, in press).

Cyclopropane and Ethylene Oxide

This Excel file (3.77 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline cyclopropane and ethylene oxide (oxirane). A full description is in Hudson, Yarnall, and Gerakines, 2023, Icarus.

Methyl Acetate

This Excel file (2.81 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline methyl acetate. A full description is in Yarnall and Hudson, 2022, Spectrochimica Acta.

Allene

This Excel file (4.45 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline allene. A full description is in Hudson and Yarnall, 2022, ACS Earth and Space Chemistry.

Methylamine and Ethylamine

This Excel file (5.57 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline methyl- and ethylamine. A full description is in Hudson, Yarnall, and Gerakine, 2022, Astrobiology.

Benzene and Pyridine

This Excel file (4.92 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline benzene and pyridine. A full description is in Hudson & Yarnall, 2022, Icarus.

Ammonia (NH3)

This Excel file (3.07 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline ammonia, NH3. A full description is in Gerakines, Yarnall, & Hudson, 2022, The Astrophysical Journal.

Hydrogen Cyanide (HCN)

This Excel file (2.64 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline hydrogen cyanide, HCN. A full description is in Gerakines, Yarnall, & Hudson, 2022, Monthly Notices of the Royal Astronomical Journal.

Nitrous Oxide (N2O)

This Excel file (10.48 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline nitrous oxide, N2O. A full description is in Gerakines & Hudson, 2020, The Astrophysical Journal.

Carbon Dioxide (CO2)

This Excel file (5.78 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline carbon dioxide, CO2. A full description is in Gerakines & Hudson, 2020, The Astrophysical Journal.

Methane (CH4)

This Excel file (5.69 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline methane, CH4. A full description is in Gerakines & Hudson, 2020, The Astrophysical Journal.

Methanol (CH3OH)

This Excel file (6.61 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline methanol, CH3OH. A full description is in Gerakines & Hudson, 2020, The Astrophysical Journal.

C3 Hydrocarbon Ices (propane, propylene, propyne)

This Excel file (19.42 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline propane, propylene, and propyne. A full description is in a manuscript of Hudson et al. 2021, accepted for publication in Icarus.

Propanal (Propionaldehyde, HC(O)CH2CH3) Ice

This Excel file (1.40 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline propanal (propionaldehyde). For details concerning temperature, spectral resolution, sample preparation, and so on, see Yarnall et al., Monthly Notices of the Royal Astronomical Society, 2020.

Dimethyl Ether (O(CH3)2) Ice

This Excel file (1.20 megabytes) has the real (n) and imaginary (k) parts of the complex index of refraction of amorphous and crystalline dimethyl ether. For details concerning temperature, spectral resolution, sample preparation, and so on, see Hudson et al., Spectrochimica Acta, 2020.

Propynal (HCC-C(=O)H) Ice

This Excel file (2.31 megabytes) has tables of the real (n) and imaginary (k) parts of the complex index of refraction of amorphous propynal at 10 K. The sample was made andinfrared spectra were recorded at 10 K. For more details, see Hudson & Gerakines, Monthly Notices of the Royal Astronomical Society, 2019, 482, 4009.

Acetone ((CH3)2CO) Ice

Links to tables of the real (n) and imaginary (k) parts of the complex index of refraction of solid acetone are given below. Note that these two files are in the Excel (xlsx) format.

Region Initial Ice Phase Temperature and Data
3600 - 500 cm-1 Amorphous 10 K
3600 - 500 cm-1 Crystalline 125 K

Methane (CH4) Ice

A link to a table of the real (n) and imaginary (k) parts of the complex index of refraction, and the transmission spectrum, of methane ice is given below. Note that the amorphous phase will crystallize on warming. — More methane data are posted above.

Region Initial Ice Phase Temperature and Data
5000 - 400 cm-1 Amorphous 10 K - spectra, n, and k

Ethane (C2H6) Ices

Links to tables of the real (n) and imaginary (k) parts of the complex index of refraction, and transmission spectra, of ethane ices are given below. Note that the amorphous and metastable ices crystallize on warming.

A copy of the paper describing this work is available as a PDF.

Region Initial Ice Phase Temperatures (K) and Data
4500 - 500 cm-1 Amorphous 16, 20, 30, 40, 50, 60
  Metastable 11, 20, 30, 40, 50 60
  Crystalline 12, 20, 30, 40, 50, 60

Ethylene (C2H4) Ices

Links to tables of the real (n) and imaginary (k) parts of the complex index of refraction, and transmission spectra, of ethylene ices are given below. Note that the amorphous and metastable ices crystallize on warming.

A copy of the paper describing this work is available as a PDF.

Region Initial Ice Phase Temperatures (K) and Data
5000 - 700 cm-1 Amorphous 12, 20, 30, 40, 50, 60
  Metastable 14, 20, 30, 40, 50, 60
  Crystalline 16, 20, 30, 40, 50, 60

Acetylene (C2H2) Ices

Links to tables of the real (n) and imaginary (k) parts of the complex index of refraction, and transmission spectra, of acetylene ices are given below. Note that there is overlap in the tables between the mid- and near-IR regions, near 3500 cm-1.

A copy of the paper describing this work is available as a PDF.

Region Ice Phase Temperatures (K) Data
Near-IR Amorphous 12, 20, 30, 40, 50, 60, 70 Spectrum n k
  Crystalline 15, 20, 30, 40, 50, 60, 70 Spectrum n k
Mid-IR Amorphous 12, 20, 30, 40, 50, 60, 70 Spectrum n k
  Crystalline 15, 20, 30, 40, 50, 60, 70 Spectrum n k

Nitrile Ices

Links to tables of the real (n) and imaginary (k) parts of the complex index of refraction of nitrile ices are given below. Note that there is overlap in the tables between the mid- and far-IR regions, near 500 cm-1.

Each table is in the machine-readable format used by The Astrophysical Journal.

A copy of the paper describing this work is available as a PDF

Nitrile
Ice
Ice Phase Temperatures (K) Data
HCN Amorphous 50, 75, 95, 110 n k
  Crystalline 20, 35, 50, 75, 95, 110, 120 n k
C2N2 Amorphous 50, 75 n k
  Crystalline 20, 35, 50, 75, 95 n k
CH3CN Amorphous 50, 75, 95, 110 n k
Crystalline 20, 35, 50, 75, 95, 110, 130 n k
C2H5CN Amorphous 50, 75, 95, 110 n k
Crystalline 20, 35, 50, 75, 95, 110, 140 n k
HC3N Amorphous 50, 75, 95 n k
Crystalline 20, 35, 50, 75, 95, 110 n k