The (j, k) = (3, 3) inversion line of NH3 - A possible interstellar chronometer

Details The (j, k) = (3, 3) inversion line of NH3 - A possible interstellar chronometer The (j, k) = (3, 3) inversion line of NH3 - A possible interstellar chronometer

May 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.244p...4f&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 244, May 1, 1990, p. 4P-8P. Research supported by SERC.

Astronomy and Astrophysics

Astronomy

18

Ammonia, Chemical Evolution, Interstellar Matter, Molecular Clouds, Abundance, Dark Matter, Density Distribution, Interstellar Masers, Molecular Collisions

Scientific paper

Calculations show that ortho-H2 and para-H2 exhibit different propensity rules in collisions with NH3. In particular, para-H2 tends to preferentially excite the upper (3 3 - ) component of the (j, k) = (3, 3) inversion doublet. Assuming collisional excitation, the existence of a maser in this transition within a molecular cloud implies an upper limit to the ratio of densities, n(o-H2)/n(p-H2). As this density ratio evolves (chemically) with time, to its upper limit there corresponds a lower limit to the age of the cloud. Calculations of the time-dependence of n(o-H2)/n(p-H2) enable this interstellar chronometer to be calibrated.

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