Vibrationally excited molecular hydrogen production from the water photochemistry.
basic_science · Level V
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- Record sourced from PubMed, PMID 34728635.
- Also identified by DOI 10.1038/s41467-021-26599-9 and PMC identifier 8563719.
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Abstract
Vibrationally excited molecular hydrogen has been commonly observed in the dense photo-dominated regions (PDRs). It plays an important role in understanding the chemical evolution in the interstellar medium. Until recently, it was widely accepted that vibrational excitation of interstellar H<sub>2</sub> was achieved by shock wave or far-ultraviolet fluorescence pumping. Here we show a further pathway to produce vibrationally excited H<sub>2</sub> via the water photochemistry. The results indicate that the H<sub>2</sub> fragments identified in the O(<sup>1</sup>S) + H<sub>2</sub>(X<sup>1</sup>Σ<sub>g</sub><sup>+</sup>) channel following vacuum ultraviolet (VUV) photodissociation of H<sub>2</sub>O in the wavelength range of λ = ~100-112 nm are vibrationally excited. In particular, more than 90% of H<sub>2</sub>(X) fragments populate in a vibrational state v = 3 at λ~112.81 nm. The abundance of water and VUV photons in the interstellar space suggests that the contributions of these vibrationally excited H<sub>2</sub> from the water photochemistry could be significant and should be recognized in appropriate interstellar chemistry models.