Population Inversion in the Outer Layers of a Radiating Gas
Abstract
On the basis of solutions to the coupled radiative transfer equations for multiplet lines, we present simple physical arguments on the expected distribution of population among closely spaced energy levels in the ground, or a low-lying state, of an atom or molecule. It is shown that, because uncoupling of multiplet lines will occur in the outer layers of a radiating gas, population "anomalies" will occur in the fine structure states associated with the upper and/or lower levels of the multiplet transitions. Order of magnitude estimates suggest that the mechanism is able to account for some aspects of the 18 cm OH emission, though better solutions of the coupled transfer equations are needed before proper observational comparison is possible. It is suggested that atoms with p and p2 configurations may be expected to have inverted populations among the ground state levels in the outer layers of an optically thick gas. A list is given of infrared and submillimetric atomic lines which may show amplification in astronomical sources. Two lines of C T are accessible to ground based (high altitude) instrumentation, and these may merit a diligent search. Key words: population inversion - radiative transfer
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 1971
- Bibcode:
- 1971A&A....12..351J