Dalian Coherent Light Source demonstrates vibrationally excited molecular hydrogen production from water photochemistry

Vibrationally excited molecular hydrogen is an essential species for determining the chemical composition in the interstellar medium.

Vibrational excited interstellar H₂ has been detected in shock-heated gas and in photodissociation regions (PDRs) near hot stars, which was formed by collisions and fluorescence excitation in PDRs.

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 (CAS) demonstrated vibrationally excited H₂ production from water photochemistry using the Dalian Coherent Light Source. This process represents a further source of vibrationally excited H₂ observed in the interstellar medium.

Their findings were published in Nature Communications on Nov. 2.

The experimental results indicated that all of the H₂ fragments identified in the O(¹S) + H₂(X¹Σ_g⁺) channel following vacuum ultraviolet photodissociation of H₂O in the wavelength range of λ=~100-112 nm were vibrationally excited. In particular, more than 90% of H₂(X) fragments populated in a single vibrational state v=3 at λ~112.81 nm.

The estimated cross section for forming H₂(v>0) fragments at λ~107.5 nm was determined to be ~3.2×10^-18 cm².

The abundance of water molecules and vacuum ultraviolet photons in the interstellar space suggested that the contributions of these H₂(v>0) sources from water photochemistry could be significant and thus should be recognized in appropriate interstellar chemistry models.

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