Webb Alexander D, Kawanaka Noboru, Dixon Richard N, Ashfold Michael N R
School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom.
J Chem Phys. 2007 Dec 14;127(22):224308. doi: 10.1063/1.2800565.
Ion imaging methods have been used to explore the photodissociation dynamics of state-selected H(2)S(+) and D(2)S(+) cations. Predissociation following one photon excitation to the A (2)A(1) state at wavelengths (385< or =lambda(phot)< or =420 nm) in the vicinity of the first dissociation threshold results in formation of ground state S(+) fragment ions; the partner H(2)(D(2)) fragments are deduced to be rotationally "cold." Two photon dissociation processes are also observed, resonance enhanced at the energy of one absorbed photon by the predissociating A state levels. Two photon excitation at these wavelengths is deduced to populate an excited state of (2)A(1) symmetry, which dissociates to electronically excited S(+)((2)D) products, together with vibrationally excited H(2)(D(2)) cofragments. Ground state SH(+)(SD(+)) fragments, attributable to a one photon dissociation process, are observed once lambda(phot)< or =325 nm. Two photon induced production of SH(+)(SD(+)) fragments is also observed, at all wavelengths studied (i.e., at all lambda(phot)< or =420 nm). These SH(+)(SD(+)) fragments are deduced to be formed in their singlet (i.e., a (1)Delta and b (1)Sigma(+)) excited states, with high levels of rotational excitation. The observed product branching and energy disposals are discussed within the context of the (limited) available knowledge relating to the excited electronic states of the H(2)S(+) cation.
离子成像方法已被用于探索态选择的H₂S⁺和D₂S⁺阳离子的光解离动力学。在接近第一个解离阈值的波长（385≤λₚₕₒₜ≤420 nm）下，单光子激发到A²A₁态后的预解离导致基态S⁺碎片离子的形成；推断其伙伴H₂（D₂）碎片的转动“冷”。还观察到双光子解离过程，在预解离的A态能级上，一个吸收光子的能量使其共振增强。推断在这些波长下的双光子激发会填充一个具有²A₁对称性的激发态，该激发态解离为电子激发的S⁺（²D）产物，以及振动激发的H₂（D₂）共碎片。当λₚₕₒₜ≤325 nm时，观察到归因于单光子解离过程的基态SH⁺（SD⁺）碎片。在所有研究的波长下（即所有λₚₕₒₜ≤420 nm），也观察到双光子诱导产生的SH⁺（SD⁺）碎片。推断这些SH⁺（SD⁺）碎片是在其单重态（即a¹Δ和b¹Σ⁺）激发态中形成的，具有高水平的转动激发。在与H₂S⁺阳离子激发电子态相关的（有限）现有知识背景下，讨论了观察到的产物分支和能量分布情况。
