Molecular line survey of Orion A from 215 to 247 GHz

Abstract

Molecular line emission from the core of the Orion molecular cloud has been surveyed from 215 to 247 GHz to an average sensitivity of about 0.2 K. A total of 544 resolvable lines were detected, of which 517 are identified and attributed to 25 distinct chemical species. A large fraction of the lines are partially blended with other identified transitions. Because of the large line width in the Orion core, the spectrum is near the confusion limit for the weakest lines identified (≈ 0.2 K). The most abundant complex molecules present are HCOOCH_3, CH_30CH_3, and C_2H_5CN, with beam-averaged column densities of about 3X10^(15) cm^(-2). Together with the simpler species S0_2, CH_30H, and CH_3CN, they account for approximately 70% of the lines in the spectrum. Relatively few unidentified lines are present. There are 27 lines clearly present in the spectrum which are currently unidentified. However, many of these are thought to be high-lying transitions of complex asymmetric rotors such as CH_30H. Present spectroscopic data are inadequate to predict the frequencies of such transitions with sufficient accuracy.

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