Detection of interstellar methyldiacetylene (CH/sub 3/C/sub 4/H)

Journal Article · Sun Jul 15 04:00:00 EDT 1984 · Astrophys. J., Lett. Ed.; (United States)

DOI:https://doi.org/10.1086/184312· OSTI ID:6176050

MacLeod, J M; Avery, L W; Broten, N W

A new interstellar molecule methyldiacetylene (CH/sub 3/C/sub 4/H) has been detected in the molecular cloud TMC-1. The J = 6..-->..5 and J = 5..-->..4 transitions have been observed in their K = 0 and K = 1 components. An assumed value of radial velocity V/sub LSR/ = +5.8 +- 0.2 km s/sup -1/ for TMC-1 yields molecular rotational constants B/sub 0/ = 2035.746 +- 0.005 MHz, D/sub J/ = 0.06 +- 0.09 kHz, and D/sub J//sub K/ = 19.8 +- 0.3 kHz, in good agreement with laboratory values. The total column density of CH/sub 3/C/sub 4/H lies in the range 2.0 x 10/sup 13/ cm/sup -2/< or =(CH/sub 3/C/sub 4/H)< or = 3 x 10/sup 13/ cm/sup -2/ for rotational temperatures from 4 K to 6 K. By comparison with CH/sub 3/C/sub 2/H, we conclude that the chemical process whereby two carbon atoms are added to the chain to make CH/sub 3/C/sub 4/H results in a decrease in abundance by a factor of 2-4, similar to the situation for linear cyanopolyynes. Because this relative abundance factor of approximately 3 is common to several different types of carbon chain molecules, we suggest that it reflects the relative abundance of pure carbon chains of different lengths. We also infer that the relative abundances (HC/sub 2/H)/(H/sub 2/) and (HC/sub 4/H)/(H/sub 2/) are 0.5 x 10/sup -6/ and 0.2 x 10/sup -6/, respectively, for TMC-1.

• Research Organization: Herzberg Institute of Astrophysics, National Research Council of Canada, Ottawa
• OSTI ID: 6176050
• Journal Information: Astrophys. J., Lett. Ed.; (United States), Journal Name: Astrophys. J., Lett. Ed.; (United States) Vol. 282:2; ISSN AJLEA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKYL RADICALS
CHEMICAL COMPOSITION
CHEMISTRY
COSMOCHEMISTRY
EMISSION SPECTRA
FREQUENCY RANGE
GHZ RANGE
GHZ RANGE 01-100
INTERSTELLAR SPACE
METHYL RADICALS
MICROWAVE SPECTRA
NITRILES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PROPIOLONITRILE
QUANTITY RATIO
RADIAL VELOCITY
RADICALS
SPACE
SPECTRA
VELOCITY