Laboratory studies of ion-neutral reactions in interstellar regions: gas-phase equilibrium between HCN and NH/sub 3/ in dense clouds
Laboratory studies have been conducted of ion-molecule reactions involved in the synthesis of NH/sub 3/, H/sub 2/O, and HCN in dense interstellar clouds, and the rate constants and product distributions for these reactions have been determined. The rate constant for the reaction NH/sub 3//sup +/+H/sub 2/..-->..NH/sub 4//sup +/+H is extremely slow at interstellar cloud temperatures, and this has some important consequences for mechanisms of NH/sub 3/ synthesis in these regions. Atomic C/sup +/ ions formed in dense clouds by the reaction He/sup +/+CO subsequently react with ammonia to produce the H/sub 2/CN/sup +/ ion, leading to the synthesis of HCN. The HCN is subsequently destroyed in turn by reaction with C/sup +/. In the case where HCN is both synthesized and destroyed by reaction of C/sup +/ ions, a simple, model-independent expression can be obtained for the relative abundances of HCN and NH/sub 3/. When we use our laboratory results for the rate constants and product distributions of the appropriate reactions, the ratio (HCN)/(NH/sub 3/)approx. =0.4 is predicted. This result in consistent with the observations. Thermoneutral exchange between H/sub 2/CN/sup +/ ions and HD is shown to be very slow, but the high (DCN)/(HCN) ratio observed in interstellar clouds (Wilson et al.) can be explained by enhancement in the (H/sub 2/D/sup +/)/(H/sub 3//sup +/) ion ratio. On this basis, a large deuterium enhancement is also predicted for the ''X-ogen'' lines, (DCO/sup +/)/(HCO/sup +/)approx. =10/sup -3/ to 10/sup -2/. (AIP)
- Research Organization:
- Jet Propulsion Laboratory, California Institute of Technology
- OSTI ID:
- 7261769
- Journal Information:
- Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 208:1; ISSN ASJOA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMMONIA
CHEMICAL REACTIONS
COLLISIONS
COSMIC RADIATION
DEUTERIUM
EQUILIBRIUM
HYDRIDES
HYDROCYANIC ACID
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
INORGANIC ACIDS
INTERSTELLAR GRAINS
ION COLLISIONS
ION-MOLECULE COLLISIONS
IONIZING RADIATIONS
ISOTOPES
LIGHT NUCLEI
MOLECULE COLLISIONS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUCLEI
ODD-ODD NUCLEI
PARTICLES
RADIATIONS
STABLE ISOTOPES
SYNTHESIS