The C3H2 2(20)-2(11) transition:  absorption in cold dark clouds.
The first observations of the 2(20)-2(11) transition of cyclopropenylidene (C3H2) at 21.6 GHz are described.  In all cases where it has been detected, the line appears in absorption, showing that this transition is "refrigerated" (i.e., Tex < 2.7 K) in cold dust clouds.  These results are compared with those for the 1(10)-1(01) transition of C3H2, and the consequences for the excitation of C3H2 qualitatively discussed.
Matthews
H E
HE
Herzberg Institute of Astrophysics, National Research Council of Canada.
Madden
S C
SC
Avery
L W
LW
Irvine
W M
WM
D055580:Astronomical Phenomena; D001256:Astronomy; D019443:Cosmic Dust; D005118:Extraterrestrial Environment; D006844:Hydrocarbons, Cyclic / Q000032:analysis*; D008872:Microwaves; D013696:Temperature
D019443:Cosmic Dust; D006844:Hydrocarbons, Cyclic