Dalian Coherent Light Source reveals origin of interstellar disulfur

Studying the creation and evolution of sulfur-containing compounds in outer space is essential for understanding interstellar chemistry. CS₂ is believed to be the most important molecule in comet nuclei, interstellar dust, or ice cores. It could produce CS and S₂ fragments after photodissociation.

The International Ultraviolet Explorer satellite only observed the emission spectra of CS and S₂, not that of CS₂. The photodissociation mechanism of CS₂ molecules remains unclear, and S₂ fragments have not been experimentally observed before.

Recently, a team led by Prof. Yuan Kaijun from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in cooperation with Prof. Wang Xing'an's group from the University of Science and Technology of China, observed the C+S₂ product channel from CS₂ photodissociation for the first time using a home-made Time-Sliced Velocity Map Ion Imaging (TS-VMI) experimental setup based on the Dalian Coherent Light Source (DCLS).

The study, published in Journal of Physical Chemistry Letters on Jan. 11, provided direct experimental evidence for the origin of the interstellar medium S₂ fragments observed previously.

The researchers investigated the two-photon ultraviolet (UV) and one-photon vacuum ultraviolet (VUV) photodissociation dynamics of CS₂ molecules via the VUV free-electron laser (FEL) at DCLS.

They directly observed the C + S₂ product channel from CS₂ photodissociation and obtained images of the electronically ground/excited states of S₂ products with vibrational excitation. The electronically-excited states of the central atom of the CS₂ molecule played an important role in the isomerization and photodissociation processes.

This research demonstrated that interstellar medium S₂ fragments could be directly generated from CS₂ photodissociation.

"Given the similarity of OCS studied in our previous works and CS₂ in this work, we believe that the central-atom elimination channel is more general than expected in the photodissociation of triatomic molecules," said Prof. Yuan.