Tag Archives: #photodissociation

Dalian Coherent Light Source Reveals Strong Isotope Effects in Photodissociation of Water Isotopolog (Chemistry)

Recently, a research group led by Prof. YUAN Kaijun and Prof. YANG Xueming from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences revealed strong isotope effects in photodissociation of the water isotopologue (HOD) using the Dalian Coherent Light Source.

Their findings were published in Science Advances on July 23.

“Our experimental results illustrate dramatically different quantum state population distributions of OH and OD fragments from HOD photodissociation. The branching ratios of the H+OD and D+OH channels display large wavelength-dependent isotopic fractionation,” said Prof. YUAN.

Because water is one of the most abundant species in the solar nebula, photodissociation of water and its isotopologue by solar vacuum ultraviolet photons may be an alternative source of the D/H isotope heterogeneity, and this effect must be considered in photochemical models.

The photochemical processes identified in this work may vary the D/H isotopic ratios in the inner and outer regions, and/or in different periods of the solar nebula, which may cause the D/H isotope heterogeneity in the solar system.

This research was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, Chemical Dynamics Research Center, and the National Natural Science Foundation of China.

Featured image: Dalian Coherent Light Source revealing strong isotope effects in water photochemistry © DICP


Reference: Zijie Luo, Yarui Zhao, Zhichao Chen, Yao Chang, Su-e Zhang, Yucheng Wu, Jiayue Yang, Yi Cheng, Li Che, Guorong Wu, Daiqian Xie, Xueming Yang, Kaijun Yuan, “Strong isotope effect in the VUV photodissociation of HOD: A possible origin of D/H isotope heterogeneity in the solar nebula”, Science Advances  21 Jul 2021: Vol. 7, no. 30, eabg7775 DOI: 10.1126/sciadv.abg7775


Provided by DICP

Dalian Coherent Light Source Reveals Oxygen Production From Three-body Photodissociation of Water (Chemistry)

The provenance of oxygen on Earth and other solar planetary bodies is a fundamental issue. It is widely accepted that the prebiotic pathway of oxygen production in the Earth primitive atmosphere was via vacuum ultraviolet (VUV) photodissociation of CO2 and subsequent recombination of two O atoms.

In contrast, the photodissociation of H2O, one of the dominant oxygen carriers, has long been assumed to proceed mainly to produce hydroxyl (OH)- and hydrogen (H)-atom primary products, and its contribution to oxygen production is limited.

Recently, a research group led by Prof. YUAN Kaijun and YANG Xueming from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences revealed oxygen production from the three-body photodissociation of water molecule using the Dalian Coherent Light Source.

Their findings were published in Nature Communications on April 30.

The VUV free-electron laser facility at the Dalian Coherent Light Source allows the researchers to quantitatively assess the importance of H2O photochemistry for oxygen production.

“Our experimental results indicated that H2O under VUV excitation can break into three fragments: one O atom and two H atoms, where the O atoms are in the 1D and 3P states. The three-body dissociation process is the dominant channel for H2O photochemistry in the 90-110 nm region,” said Prof. YUAN.

The quantitative determination demonstrated that approximately 20% of the H2O photoexcitation events resulted in O atoms. Considering the water abundance in widely interstellar circumstances such as in interstellar clouds, atmospheres of the solar-family comets, and even in the Earth primitive atmosphere, O production from water photolysis must be an important process. The subsequent recombination of O atoms produced O2, which represented an important prebiotic O2-production pathway.

This research was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, Chemical Dynamics Research Center, and the National Natural Science Foundation of China.

Featured image: Dalian Coherent Light Source revealing three-body photodissociation of water as an important prebiotic-O2 source


Reference: Chang, Y., Yu, Y., An, F. et al. Three body photodissociation of the water molecule and its implications for prebiotic oxygen production. Nat Commun 12, 2476 (2021). https://doi.org/10.1038/s41467-021-22824-7


Provided by Dalian Institute of Chemical Physics

Dalian Coherent Light Source Reveals the Origin of Interstellar Medium S2 Fragments (Chemistry)

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. CS and S2 are the photodissociation fragments of CS2.

Forty years ago, the emission spectra of only CS and S2 species, and not those of CS2 species, were observed from several comets by the International Ultraviolet Explorer satellite. 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).

This study, published in The Journal of Physical Chemistry Letters on January 11 2021, 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.

Moreover, the researchers analyzed the product scattering anisotropy parameter β value. 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,” stated Prof YUAN.

This work was supported by the Chemical Dynamics Research Center, the National Natural Science Foundation of China, and the Key Technology Team of CAS.

Featured image: Researchers Directly Observed the C + S2 Channel in CS2 Photodissociation © DICP


Reference: Zhenxing Li, Min Zhao, Ting Xie, Zijie Luo, Yao Chang, Gongkui Cheng, Jiayue Yang, Zhichao Chen, Weiqing Zhang, Guorong Wu, Xingan Wang, Kaijun Yuan, and Xueming Yang, “Direct Observation of the C + S2 Channel in CS2 Photodissociation”, J. Phys. Chem. Lett. 2021, 12, 2, 844–849. https://doi.org/10.1021/acs.jpclett.0c03386


Provided by Dalian Institute of Chemical Physics, Chinese Academy of Sciences