Ratio of carbon monoxide to molecular hydrogen in interstellar dark clouds

Journal Article · Tue Aug 01 04:00:00 EDT 1978 · Astrophys. J., Suppl. Ser.; (United States)

DOI:https://doi.org/10.1086/190535· OSTI ID:6688089

Dickman, R L

Carbon monoxide and molecular hydrogen column densities are compared at various locations within 38 interstellar dark clouds. CO column densities were obtained from radio observations of the J=1..-->..0 transitions of the /sup 12/C/sup 16/O and /sup 13/C/sup 16/O isotopic species of the molecule. Corresponding H/sub 2/ column densities were inferred by means of visual extinctions derived from star counts, since it is argued that the standard gas-to-extinction ratio can be expected to remain valid in the clouds studied. For locations in the sources possessing line-of-sight visual extinctions in the approximate range 1.5< or approx. =A/sub ..nu../< or approx. =10mag, we find, on the average, the relationship N/sub H2/(cm/sup -2/) = (5.0 +- 2.5) x 10/sup 5/N/sub 13/ between molecular hydrogen and /sup 13/CO LTE column densities. The carbon monoxide molecule can therefore be used as a quantitative ''tracer'' for the (directly unobservable) H/sub 2/ content of dark clouds. The above relationship implies that at least approx.12% of the gas-phase carbon in the clouds studied is in the form of CO, provided that the clouds are assumed to be chemically homogeneous. Langer's ion-molecule chemistry for dark clouds appears to agree well with the present work if the fractionation channel of Watson, Anicich, and Huntress is included.

• Research Organization: Physics Department, Columbia University; Rensselaer Polytechnic Institute; and The Ivan A. Getting Laboratories, The Aerospace Corporation
• OSTI ID: 6688089
• Journal Information: Astrophys. J., Suppl. Ser.; (United States), Journal Name: Astrophys. J., Suppl. Ser.; (United States) Vol. 37:4; ISSN APJSA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
COSMIC DUST
COSMOCHEMISTRY
CRYOGENIC FLUIDS
DUSTS
ELEMENTS
ENERGY-LEVEL TRANSITIONS
EQUILIBRIUM
FLUIDS
FUNCTIONS
HYDROGEN
INTERSTELLAR GRAINS
INTERSTELLAR SPACE
ISOTOPE RATIO
LTE
MOLECULES
NEBULAE
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PARTICLES
SPACE
SPECTRAL FUNCTIONS