- Names
-
- B.~M. Giuliano
- R.~M. Escribano
- R. Martin-Doménech
- E. Dartois
- G.~M. Munoz Caro
- Title
- Interstellar ice analogs: band strengths of H$_2$O, CO$_2$, CH$_3$OH, and NH$_3$ in the far-infrared region
- Abstract
- Context. Whereas observational astronomy now routinely extends to the far-infrared region of the spectrum, systematic laboratory studies are sparse. In particular, experiments on laboratory analogs performed through the years have provided information mainly about the band positions and shapes, while information about the band strengths are scarce and derivable principally from the optical constants. - Aims: We measure the band strengths in the far-infrared region of interstellar ice analogs of astrophysically relevant species, such as H$_2$O, CO$_2$, CH$_3$OH, and NH$_3$, deposited at low temperature (8-10 K), followed by warm-up, to induce amorphous-crystalline phase transitions when relevant. - Methods: The spectra of pure H$_2$O, NH$_3$, and CH$_3$OH ices have been measured in the near-, mid- and far-infrared spectroscopic regions using the Interstellar Astrochemistry Chamber (ISAC) ultra-high-vacuum setup. In addition, far-infrared spectra of NH$_3$ and CO$_2$ were measured using a different set-up equipped with a bolometer detector. Band strengths in the far- infrared region were estimated using the corresponding near- and mid-infrared values as a reference. We also performed theoretical calculations of the amorphous and crystalline structures of these molecules using solid state computational programs at density functional theory (DFT) level. Vibrational assignment and mode intensities for these ices were predicted. -Results: Infrared band strengths in the 25-500 \ensuremathμm range have been determined for the considered ice samples by direct comparison in the near- and mid-infrared regions. Our values were compared to those we calculated from the literature complex index of refraction. We found differences of a factor of two between the two sets of values. - Conclusions: The calculated far-infrared band strengths provide a benchmark for interpreting the observational data from future space telescope missions, allowing the estimation of the ice column densities.
- Keywords
- spectroscopy, transmission spectra, band position, band vibration mode, mid-IR, far-IR, molecular solid, molecular liquid, CH3OH, H2O, CO2, NH3, ices, Astrophysics
- Content
- spectral data, band list data, astrophysics
- Year
- 2014
- Journal
- Astronomy and Astrophysics
- Volume
- 565
- Pages
- A108
- Pages number
- 7
- Document type
- article
- Publication state
- published
- Doi
- 10.1051/0004-6361/201423560
- Identifiers
-
- bibcode: 2014A&A...565A.108G