Methyl cyanide hot and warm cores in Orion: Statistical equilibrium excitation models of a symmetric-top molecule

Journal Article · Thu Nov 01 04:00:00 EST 1984 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/162591· OSTI ID:5924547

Loren, R B; Mundy, L G

More than 50 lines of the symmetric-top molecule CH/sub 3/CN, from J = 6--5 up to J = 16--15 and components from K = 0 to K = 7, have been observed toward OMC-1. High-velocity resolution line profiles reveal two kinematically and thermally distinct regions; broad emission (..delta..Vapprox.12 km s/sup -1/) at 5.1 km s/sup -1/ arising from an unresolved hot core and narrow emission (..delta..Vapprox.4 km s/sup -1/) at 8.7 km s/sup -1/ arising from dense warm clumps of the quiescent cloud. Statistical equilibrium models fitted to the resolved K = 3 and K = 6 A species line profiles yield kinetic temperatures for the regions emitting the broad and narrow components of 275 +- 25 K and 95 +- 8 K, respectively. The CH/sub 3/CN abundance is enhanced in the hot core by a factor of at least 10 relative to the quiescent cloud. The excitation of the statistical equilibrium (SE) models is compared to that predicted by the rotational temperature equilibrium (RTE) analytic method. The RTE method can accurately predict T/sub k/ for both of the nearly thermalized regions in OMC-1 when T/sub rot/ is determined from levels which span a large range of J, but not with Hollis's 1982 method of determining T/sub rot/ from adjacent J levels. For high-temperature CH/sub 3/CN regions the RTE method fails to correctly predict T/sub k/ in the density range from 10/sup 2.5/ cm/sup -3/ to 10/sup 6/ cm/sup -3/ which commonly occurs in molecular clouds.

• Research Organization: Millmeter Wave Observatory, Electrical Engineering Research Lab., The University of Texas at Austin
• OSTI ID: 5924547
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 286:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKYL RADICALS
EMISSION SPECTRA
ENERGY LEVELS
ENERGY-LEVEL DENSITY
ENERGY-LEVEL TRANSITIONS
EXCITATION
INTERSTELLAR GRAINS
LINE WIDTHS
MATHEMATICAL MODELS
MECHANICS
METHYL RADICALS
NEBULAE
PARTICLES
QUANTUM MECHANICS
RADICALS
SPECTRA
STATISTICAL MODELS
SYMMETRY