Formaldehyde in giant molecular clouds - H2 densities and corrections to the C-12/C-13 ratios

Details Formaldehyde in giant molecular clouds - H2 densities and corrections to the C-12/C-13 ratios Formaldehyde in giant molecular clouds - H2 densities and corrections to the C-12/C-13 ratios

Feb 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980a%26a....82...41h&link_type=abstract

Astronomy and Astrophysics, vol. 82, no. 1-2, Feb. 1980, p. 41-47.

Astronomy and Astrophysics

Astronomy

65

Abundance, Carbon Isotopes, Formaldehyde, Galactic Structure, Hydrogen Clouds, Molecular Gases, Data Reduction, Galactic Nuclei, Isotope Effect, Line Spectra, Microwave Spectra, Radio Astronomy

Scientific paper

Measurements of the 211-212 line of H2CO, at 14.5 GHz, toward 10 strong galactic continuum sources are presented. The angular resolution of the 14.5 GHz data was broadened to 2'.6, and compared with the 110-111 results, at 4.8 GHz, of Wilson et al. (1976). From these measurements, the H2CO collision rates of Green et al. (1978) and an LVG treatment of the radiative transfer, we have estimated the density of H2 and the correction to the (12C/13C) ratio obtained from the 110-111 lines of H212CO and H213CO. The H2 densities in these molecular clouds cluster around 105 cm-3 and the average correction factor for the isotope ratio is 1.6±0.7. The average corrected (12C/13C) ratio is 64±17, which is not significantly different from the terrestrial value, 89. There is a gradient as a function of distance from the galactic center in both the corrected and uncorrected (12C/13C) ratios, but we do not believe this to be very significant. The average (12C/13C) ratios differ from those ratios determined from (12C15O/ 13C16 O). This may imply fractionation in 13CO.

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