Absorption against the cosmic 2.7 K background

¹ School of Physical Sciences, S.R.T.M. University, Nanded 431 606, India
² Institut für Theoretische Physik, J.W. Goethe-Universität, 60054 Frankfurt am Main, Germany

Corresponding author: W. H. Kegel, kegel@astro.uni-frankfurt.de

Received: 25 February 2000
Accepted: 12 December 2000

Abstract

Two interstellar lines, 1 1₁₁ of formaldehyde at 4.831 GHz, and 2 2₁₁ of cyclopropenylidene at 21.590 GHz, have so far been observed in absorption against the cosmic 2.7 K background. Observation of an interstellar line in absorption against the cosmic 2.7 K background is an unusual phenomenon, and can only be possible under rather peculiar conditions developed in the molecule, generating the line. We predict that two more lines, 3 3₂₁ at 27.100 GHz, and 3 3₂₂ at 59.550 GHz of cyclopropenylidene, and three lines, 2 2₁₁ at 15.600 GHz, 3 3₂₁ at 23.100 GHz, and 3 3₂₂ at 39.700 GHz of ethylene oxide, may show absorption against the cosmic 2.7 K background. We speculate that such peculiar conditions are characteristic for b-type asymmetrical top molecules. -The observation of these lines may be used to place upper bounds to the density in the absorbing region.