Photodissociation dynamics of H₂S⁺ via A²A₁(1, 8, 0) excited state^†

Excitation of vibration plays an important role in the photodissociation dynamics of molecules and ions. Experiments on the photodissociation dynamics of molecular ions via well-defined excited vibrational states present a formidable challenge, particularly when it comes to the selective preparation of ions at the vibrational combination level. Here, using time-sliced velocity map ion imaging, the photodissociation of H₂S⁺ via A²A₁(v₁=1, v₂=8, v₃=0, K=1) state leading to S⁺(⁴S) and H₂ products was investigated. The excited H₂S⁺ cations were prepared by multiphoton ionization of H₂S, followed by resonant excitation. Images of S⁺ ions were captured at six wavelengths ranging from 357.02 nm to 358.38 nm. From the ion images, the total kinetic energy release distributions and rotational state-specific anisotropy parameters were derived. Notably, repeatedly reversed branching ratios of the H₂ (J=1) and H₂ (J=3) rotational states were observed in a narrow photolysis energy region. This behavior was totally different from the results in recent studies on the photodissociation of H_S⁺ where only a single vibrational mode v₂ was excited for parent ions in A²A₁(v₁, v₂, v₃) states. The present study indicates that potential vibrational synergy effect was observed in the photodissociation dynamics of H₂S⁺ when the parent ions were excited in a combinational vibrational mode.