# Searches for Interstellar HCCSH and H$_2$CCS

## TL;DR

This study conducted radioastronomical searches for interstellar sulfur-containing hydrocarbons HCCSH and H$_2$CCS, but found no evidence of their presence in various space environments, suggesting they are not major sulfur reservoirs there.

## Contribution

The paper provides the first laboratory spectral data for HCCSH and H$_2$CCS and reports comprehensive astronomical searches resulting in non-detections, refining sulfur chemistry models.

## Key findings

- No detections of HCCSH or H$_2$CCS in surveyed environments.
- Upper abundance limits are between 10^{-9} and 10^{-10}.
- Neither species appears to be a major sulfur reservoir in studied regions.

## Abstract

A long standing problem in astrochemistry is the inability of many current models to account for missing sulfur content. Many relatively simple species that may be good candidates to sequester sulfur have not been measured experimentally at the high spectral resolution necessary to enable radioastronomical identification. On the basis of new laboratory data, we report searches for the rotational lines in the microwave, millimeter, and sub-millimeter regions of the sulfur-containing hydrocarbon HCCSH. This simple species would appear to be a promising candidate for detection in space owing to the large dipole moment along its $b$-inertial axis, and because the bimolecular reaction between two highly abundant astronomical fragments (CCH and SH radicals) may be rapid. An inspection of multiple line surveys from the centimeter to the far-infrared toward a range of sources from dark clouds to high-mass star-forming regions, however, resulted in non-detections. An analogous search for the lowest-energy isomer, H$_2$CCS, is presented for comparison, and also resulted in non-detections. Typical upper limits on the abundance of both species relative to hydrogen are $10^{-9}$-$10^{-10}$. We thus conclude that neither isomer is a major reservoir of interstellar sulfur in the range of environments studied. Both species may still be viable candidates for detection in other environments or at higher frequencies, providing laboratory frequencies are available.