Unraveling the Rich Fragmentation Dynamics Associated with S-H Bond Fission Following Photoexcitation of H 2 S at Wavelengths ∼129.1 nm.

H 2 S is being detected in the atmospheres of ever more interstellar bodies, and photolysis is an important mechanism by which it is processed. Here, we report H Rydberg atom time-of-flight measurements following the excitation of H 2 S molecules to selected rotational ( J KaKc ') levels of the 1 B 1 Rydberg state associated with the strong absorption feature at wavelengths of λ ∼ 129.1 nm. Analysis of the total kinetic energy release spectra derived from these data reveals that all levels predissociate to yield H atoms in conjunction with both SH(A) and SH(X) partners and that the primary SH(A)/SH(X) product branching ratio increases steeply with ⟨ J b 2 ⟩, the square of the rotational angular momentum about the b -inertial axis in the excited state. These products arise via competing homogeneous (vibronic) and heterogeneous (Coriolis-induced) predissociation pathways that involve coupling to dissociative potential energy surfaces (PES(s)) of, respectively, 1 A″ and 1 A' symmetries. The present data also show H + SH(A) product formation when exciting the J KaKc ' = 0 00 and 1 11 levels, for which ⟨ J b 2 ⟩ = 0 and Coriolis coupling to the 1 A' PES(s) is symmetry forbidden, implying the operation of another, hitherto unrecognized, route to forming H + SH(A) products following excitation of H 2 S at energies above ∼9 eV. These data can be expected to stimulate future ab initio molecular dynamic studies that test, refine, and define the currently inferred predissociation pathways available to photoexcited H 2 S molecules.