Measurement and significance of the reaction 13C++12CO ü 12C++13CO for alteration of the 13C/12C ratio in interstellar molecules.
Abstract
Laboratory measurements using the ion-cyclotron resonance technique yield a rate constant of 2 by 10 to the -10th power cu cm/sec at 300 K for the isotope exchange C-13(+) + (C-12)O yields C-12(+) + (C-13)O. According to the usual ideas about ion-molecule reactions, this rate constant should also be appropriate at temperatures not exceeding about 100 K. Then the observed C-13/C-12 ratio obtained from radio observation of interstellar molecules may be either larger or smaller than the actual value in the interstellar medium by factors of 2 or so. If the ratio is altered from the actual interstellar value, it will not be the same in all molecules, and CO will tend to have the highest value. The chief astronomical uncertainty for the occurrence of this isotope fractionation is the abundance of 'unobservable' molecules which can react rapidly with C(+): e.g., O2, H2O, CO2, and CH4. If their abundance is greater than about one-tenth that of CO, the isotope fractionation will be inhibited.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 1976
- DOI:
- 10.1086/182115
- Bibcode:
- 1976ApJ...205L.165W
- Keywords:
-
- Chemical Equilibrium;
- Interstellar Matter;
- Molecular Gases;
- Molecular Interactions;
- Reaction Kinetics;
- Abundance;
- Carbon Isotopes;
- Cyclotron Resonance;
- Interstellar Gas;
- Ion Cyclotron Radiation;
- Ionic Reactions;
- Nuclear Fusion;
- Astrophysics