Photodissociation of H₂S: A New Pathway for the Production of Vibrationally Excited Molecular Hydrogen in the Interstellar Medium

Abstract

Hydrogen sulfide (H2S) is the most abundant S-bearing molecule in the solar nebula. Although its photochemistry has been studied for decades, the H2 fragment channel is still not well-understood. Herein, we describe the photodissociation dynamics of H2S + hv → S(1S) + H2(X1Σg+) with the excitation wavelength of 122 nm ≤ λ ≤ 136 nm. The results reveal that the H2(X) fragments formed are significantly vibrationally excited, with the quantum yields of ∼87% of H2(X) fragments populated in vibrational levels v″ = 3, 4, 5, and 6. Theoretical analysis suggest that these H2 products are formed on the H2S 41A′ state surface following a nonadiabatic transition via an avoided crossing from the 31A′ to 41A′ state. The estimated quantum yield of the S(1S) + H2 channel is ∼0.05, implying this channel should be incorporated into the appropriate interstellar chemistry models.