title: H2CS abundances and ortho-to-para ratios in interstellar clouds.
abstract: Several H2CS ortho and para transitions have been observed toward interstellar molecular clouds, including cold, dark clouds and star-forming regions.  We derive H2CS fractional abundances f(H2CS) approximately 1-2 10(-9) relative to molecular hydrogen towards TMC-1, Orion A, and NGC 7538, and approximately 5 10(-10) for L134N.  The H2CS ortho-to-para ratios in TMC-1 are approximately 1.8 towards the cyanopolyyne peak and the ammonia peak, which may indicate the thermalization of H2CS on 10 K grains.  We derive a ratio of approximately 3, the statistical value, for Orion (3N, 1E) and NGC 7538, while we find a value approximately 2 for Orion (KL).
authors.affiliation: Department of Physics and Astronomy, University of Massachusetts, Amherst 01003, USA.
authors.forename: Y C
authors.initials: YC
authors.lastname: Minh
authors.forename: W M
authors.initials: WM
authors.lastname: Irvine
authors.forename: M K
authors.initials: MK
authors.lastname: Brewer
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D005557:Formaldehyde / Q000031:analogs & derivatives*; D006859:Hydrogen / Q000737:chemistry; D008956:Models, Chemical; D016082:Solar System; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D005557:Formaldehyde; D006859:Hydrogen