Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.......394s&link_type=abstract
PhD Thesis, Max-Planck-Institut für Radioastronomie, Bonn, Germany, 1992.
Astronomy and Astrophysics
Astronomy
1
Scientific paper
The main results of this thesis are as follows [i)] The molecular ion HCNH+ has been detected in the dark cloud TMC-1. This is the first detection of this molecule outside the galactic center. The hyperfine structure has been resolved and shown to be similar to HNC. The analysis of the data has shown that the HCNH+ / HCN ratio is very high, as compared e.g. to the HCO+ / CO ratio (≅3 10-2 vs. 10-4). [ii)] The high [HCNH+]/[HCN] ratio could be successfully reproduced by gas phase chemical models. The best agreement with observations is achieved in models with a very high metal depletion ratio ([M]/[H] ≅10-11), consistent with the non-detection of silicon bearing species in this source. [iii)] The source OMC-1 has been mapped in HCN, HNC and some isotopomers with the IRAM 30 m telescope. The derived [HCN]/[HNC] and [DCN]/[HCN] ratios differ drastically from the hot core region to the ridge. HNC and, to a lesser degree, DCN, seem to avoid the star forming region around the infrared source IRc2, while they trace nicely the filamentary structure in the north of the hot core. But even in the ridge, the [HCN]/[HNC] ratio is significantly different from that of a dark cloud. The [DCN]/[HCN] ratio there is surprisingly high, given the kinetic temperatures of about 40 K and densities of about 106 cm-3. [iv)] Complementary, the hot core region was observed with the Plateau de Bure Interferometer in the HC15N(1-0) transition. It has been shown, mapping for the first time an optically thin transition in the millimeter--range, that HCN is concentrated on the hot core. The simultaneously obtained continuum data allowed a H2 column density determination in the hot core. The HCN abundance has been derived to be about 100-300 times higher than in the ridge. A comparison with a BIMA DCN(1-0) revealed that the [DCN]/[HCN] ratio is about 10 times lower than in the ridge. [v)] Chemical modelling showed that the ridge results for the [HCN]/[HNC] ratio can be successfully modelled by means of steady state gas phase chemistry of warm, dense gas. The most important assumption in this model is that HNC can be destroyed at high temperatures in reactions with atomic oxygen. The high [DCN]/[HCN] ratio could be explained without further assumptions to be due to neutral--neutral reactions which play no role in less dense gas. By investigating gas phase chemistry with CNO depletion (to model regions where the the gas freezes out onto grains), it could be shown that CNO depletion larger than about 100 (relative to solar abundances) can definitely be ruled out. The observed HCN abundance seems to favour models with a higher [C]/[CO] ratio than predicted by standard models. [vi)] The extremely high [HCN]/[HNC] ratio in the hot core could be due to influence of magnetohydrodynamic shocks or due to release of grain--surface chemistry processed ice mantles. While the results of our shock chemistry models predict a [DCN]/[HCN] ratio which is close to thet observed, the grain surface chemistry models from the literature would give ratio which is much too high. A realistic model of the region should therefore allow for both processes taking place, i.e. postprocessing of the released molecules.
No associations
LandOfFree
The Chemistry of Interstellar Hydrogen Cyanide: Observations and Theory 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 The Chemistry of Interstellar Hydrogen Cyanide: Observations and Theory, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Chemistry of Interstellar Hydrogen Cyanide: Observations and Theory will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1490612