Discovery of H$_2$CCCH$^+$ in TMC-1

TL;DR

This paper reports the first detection of the molecular ion H$_2$CCCH$^+$ in the TMC-1 cloud, combining laboratory spectroscopy, astronomical observations, and chemical modeling to understand its abundance and role in interstellar chemistry.

Contribution

The study provides high-precision laboratory measurements of H$_2$CCCH$^+$ spectra and reports its detection in space, advancing understanding of C$_3$-bearing molecules in interstellar environments.

Findings

Detected four lines of H$_2$CCCH$^+$ in TMC-1.

Derived column densities and abundance ratios for H$_2$CCCH$^+$.

Modelled the chemistry of H$_2$CCCH$^+$ with reasonable agreement to observations.

Abstract

Based on a novel laboratory method, 14 mm-wave lines of the molecular ion H$_2$CCCH$^+$ have been measured in high resolution, and the spectroscopic constants of this asymmetric rotor determined with high accuracy. Using the Yebes 40 m and IRAM 30 m radio telescopes, we detect four lines of H$_2$CCCH$^+$ towards the cold dense core TMC-1. With a dipole moment of about 0.55 Debye obtained from high-level ab initio calculations, we derive a column density of 5.4$\pm$1$\times$10$^{11}$ cm$^{-2}$ and 1.6$\pm$0.5$\times$10$^{11}$ cm$^{-2}$ for the ortho and para species, respectively, and an abundance ratio N(H$_2$CCC)/N(H$_2$CCCH$^+$)= 2.8$\pm$0.7. The chemistry of H$_2$CCCH$^+$ is modelled using the most recent chemical network for the reactions involving the formation of H$_2$CCCH$^+$. We find a reasonable agreement between model predictions and observations, and new insights into the chemistry of C$_3$ bearing species in TMC-1 are obtained.