High spectral resolution observations of HNC3 and HCCNC in the L1544 prestellar core

TL;DR

This study reports the detection of HNC3 in the prestellar core L1544, providing new spectroscopic data and comparing observed molecular abundances with chemical models to understand their formation and distribution.

Contribution

The paper presents the first detection of HNC3 in L1544, along with new spectroscopic parameters and a comparison of molecular abundances with chemical models in a prestellar core.

Findings

HNC3 detected in L1544 prestellar core.

Model predictions are consistent with observations, except for HNC3 abundance.

Comparison of molecular ratios between L1544 and TMC-1.

Abstract

HCCNC and HNC3 are less commonly found isomers of cyanoacetylene, HC3N, a molecule that is widely found in diverse astronomical sources. We want to know if HNC3 is present in sources other than the dark cloud TMC-1 and how its abundance is relative to that of related molecules. We used the ASAI unbiased spectral survey at IRAM 30m towards the prototypical prestellar core L1544 to search for HNC3 and HCCNC which are by-product of the HC3NH+ recombination, previously detected in this source. We performed a combined analysis of published HNC3 microwave rest frequencies with thus far unpublished millimeter data because of issues with available rest frequency predictions. We determined new spectroscopic parameters for HNC3, produced new predictions and detected it towards L1544. We used a gas-grain chemical modelling to predict the abundances of N-species and compare with the observations. The modelled abundances are consistent with the observations, considering a late stage of the evolution of the prestellar core. However the calculated abundance of HNC3 was found 5-10 times higher than the observed one. The HC3N, HNC3 and HCCNC versus HC3NH+ ratios are compared in the TMC-1 dark cloud and the L1544 prestellar core.