Combined IRAM and<i>Herschel</i>/HIFI study of cyano(di)acetylene in Orion KL: tentative detection of DC₃N

Abstract

Received; accepted Context. We present a study of cyanoacetylene (HC3N) and cyanodiacetylene (HC5N) in Orion KL, through observations from two lines surveys performed with the IRAM 30-m telescope and the HIFI instrument on board the Herschel telescope. The frequency ranges covered are 80-280 GHz and 480-1906 GHz. Aims. This study (divided by families of molecules) is part of a global analysis of the physical conditions of Orion KL, as well as molecular abundances in the different components of this cloud. Methods. We modeled the observed lines of HC3N, HC5N, their isotopologues (including DC3N), and vibrational modes, using a non-LTE radiative transfer code. In addition, to investigate the chemical origin of HC3N and DC3N in Orion KL, we have used a time-dependent chemical model. Results. We detect 40 lines of the ground vibrational state of HC3N and 68 lines of its 13C isotopologues. We also detect 297 lines of six vibrational modes of this molecule (ν7, 2ν7, 3ν7, ν6, ν5, and ν6+ν7) and 35 rotational lines of the ground vibrational state of HC5N. We report the first tentative detection of DC3N in a giant molecular cloud. We have obtained a DC3N/HC3N abundance ratio of 0.015±0.009, comparable to typical D/H ratios of cold dark clouds. We provide column densities for all species and derived isotopic and molecular abundances. We have also performed a 2′×2 ′ map around Orion IRc2 and we present maps of HC3N lines with energies