IR-Action Spectroscopy of the Astrochemically Relevant HCCS⁺ Cation

Area of Science:

• Astrochemistry
• Chemical Physics
• Spectroscopy

Background:

• The thioketenyl cation (HCCS+) has been detected in interstellar clouds.
• Its infrared (IR) spectrum is needed for astronomical searches, including exoplanets.
• Current spectroscopic data for HCCS+ is lacking.

Purpose of the Study:

• To obtain the first experimental infrared spectrum of the HCCS+ ion.
• To provide essential spectroscopic reference data for astronomical observations.
• To aid in the identification and study of HCCS+ in various cosmic environments.

Main Methods:

• Selective generation of HCCS+ in its triplet ground state.
• Infrared photodissociation (IR-PD) spectroscopy using a cryogenic 22-pole ion trap and FELIX light source.
• Complementary theoretical calculations (ab initio) for spectral assignment and fragmentation analysis.

Main Results:

• The IR-action spectrum of H2-tagged HCCS+ was measured in two key wavenumber regions.
• Experimental vibrational bands were assigned by comparison with theoretical calculations.
• Good agreement was found between experimental and scaled theoretical spectra.

Conclusions:

• The generated IR spectrum provides the first experimental reference for HCCS+.
• This data will enable JWST searches for HCCS+ in molecular clouds and exoplanetary atmospheres.
• Findings facilitate future reactivity studies and inclusion in astrochemical models.