The Neutral Carbon Content in Cool Molecular Clouds

Details The Neutral Carbon Content in Cool Molecular Clouds The Neutral Carbon Content in Cool Molecular Clouds

Nov 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dln.........30s&link_type=abstract

Daresbury Laboratory: Newsletter on Analysis of Astronomical Spectra, p. 30

Other

Carbon, Chemical Composition, Molecular Clouds, Fine Structure, Hydrogen, Isotopes, Ground State, Sensitivity, Coefficients, Drying

Scientific paper

Neutral carbon has a P-3 ground state which splits through spin-orbit coupling into (3)Po, (3)P1, and (3)P2 fine structure levels with energies at 0, 23, and 63 K, respectively. These levels are readily excited for temperatures TK approximately equals 15-40 K which are common in the cool ISM. The corresponding fine structure transitions are at 492 and 810 GHz. The [C 1] 492 GHz spectra are often compared with those of low-level CO rotational lines since they have comparable Einstein A-coefficients and comparable cross-sections for collisions with H2 (the main collision partner). Carbon is a key building block in chemical networks, and its abundance in molecular clouds is important for the formation of carbon bearing molecules other than CO. Therefore, observations of [C 2], [C 1], CO and their isotopes provide valuable tests for the chemical models. Until recently neutral carbon could only be observed in high density, high intensity PDRs. With the advent of sensitive SIS detectors and antennas with a high surface accuracy, it has become possible to extend-the [C 1] line studies to cool molecular clouds from high-dry sites like Mauna Kea, Gornergrat, the South-Pole, and Mt. Graham.

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