Ammonium and formate ions in interstellar ice analogues. Ice morphology and the elusive 6.85 μm band.

Details Ammonium and formate ions in interstellar ice analogues. Ice morphology and the elusive 6.85 μm band. Ammonium and formate ions in interstellar ice analogues. Ice morphology and the elusive 6.85 μm band.

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.197h&link_type=abstract

The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole

Other

Scientific paper

Tentative identifications of ions in interstellar ices, based on mid IR spectra, have been reported in the literature for about two decades, but these identifications remain often vague or controversia. NH4+ and HCOO- are among the purportedly identified ions. In particular the ν4 deformation mode of NH4+ has been put forward as a firm candidate for the ubiquitous 6.85 μm band. For the generation of the ions in laboratory ice mixtures the samples are often processed with high energy photons or charged particles. On other occasions acid-base reactions of suitable precursors, which can be very efficient even at very low temperatures, are employed. These procedures, can shed light on astrophysical generation pathways, but can also lead to uncertainties in the assignment of newly formed spectral bands to a given species. In this work we have used a different approach. To minimize ambiguity we produce directly (compact) ice samples containing the ions of interest through the sudden freeze of aqueous solution droplets of NH4Cl, NaCOOH, and NH4COOH on a cold (14 K) Si substrate, where their spectra are recorded. In complementary experiments, NH4+ and HCOO- ions are produced through acid-base reactions in (porous) ices formed by co-deposition of H2O, NH3 and HCOOH. The comparison of the ice spectra with those of liquid solutions, solid salts, and DFT calculations indicate that the ν4 band of ammonium ions embedded in compact ice becomes very broad and disappears virtually. The broadening effect is also present, though not so marked, for HCCO-. In the porous ices there seems to be a segregation of NH4+HCOO- ionic networks from the ice that gives rise to more pronounced spectral features. We conclude that NH4+ is not a likely carrier for the prominent 6.85 μm band in the compact ices often assumed for the interstellar grain mantles.

Affiliated with

Also associated with

No associations

Rating

Ammonium and formate ions in interstellar ice analogues. Ice morphology and the elusive 6.85 μm band. does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Ammonium and formate ions in interstellar ice analogues. Ice morphology and the elusive 6.85 μm band., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ammonium and formate ions in interstellar ice analogues. Ice morphology and the elusive 6.85 μm band. will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-929662