Photoelectron spectroscopy of HCCS radical

Linear carbon chains are an important family of molecules detected in various astrophysical environments. In this work, we investigate the vacuum ultraviolet photoionization of HCCS, the smallest sulfur-bearing carbon chain in the HCnS family. The radical is produced from thiirane in situ in a flow-tube reactor coupled to a microwave discharge. The vibronic structures are assigned using ab initio calculations. The adiabatic ionization energies toward the ground (X+Σ-3) and first electronic excited (a+Δ1) states of the cation are measured experimentally for the first time at 9.191 ± 0.003 and 9.856 ± 0.003 eV, respectively, while a tentative value of 10.364 ± 0.006 eV is offered for the b+Σ+1 state.