Photodissociation of H 2 S: A New Pathway for the Production of Vibrationally Excited Molecular Hydrogen in the Interstellar Medium.

Hydrogen sulfide (HS) is the most abundant S-bearing molecule in the solar nebula. Although its photochemistry has been studied for decades, the H fragment channel is still not well-understood. Herein, we describe the photodissociation dynamics of HS + → S(S) + H(XΣ) with the excitation wavelength of 122 nm ≤ λ ≤ 136 nm. The results reveal that the H(X) fragments formed are significantly vibrationally excited, with the quantum yields of ∼87% of H(X) fragments populated in vibrational levels ″ = 3, 4, 5, and 6. Theoretical analysis suggest that these H products are formed on the HS 4' state surface following a nonadiabatic transition via an avoided crossing from the 3' to 4' state. The estimated quantum yield of the S(S) + H channel is ∼0.05, implying this channel should be incorporated into the appropriate interstellar chemistry models.