用能量分辨光离子角分布区分9.3 eV飞秒脉冲双光子吸收后O $_2$中离子对形成的共振对称性
Distinguishing resonance symmetries with energy-resolved photoion angular distributions from ion-pair formation in O$_2$ following two-photon absorption of a 9.3 eV femtosecond pulse
摘要：
我们提出了一个相结合的实验和理论研究O $_2$离子对形成的光解动力学的共振双光子吸收的9.3 eV的飞秒脉冲，其中产生的O $^+$离子检测使用3-D动量成像。离子对形成状态的$^3Σ^-_g$和$^3Π_g$对称性的访问通过预解离的光学暗连续里德堡态收敛到B $^2Σ^-_g$离子状态，这是共振填充通过混合的平行-平行和平行-垂直双光子跃迁。这种混合物在解离相对于光偏振的角分布中是明显的，并且随着碎裂离子对的动能释放（KER）而变化。依赖于KER的光离子角分布揭示了离子对产生机制中所涉及的基本双光子吸收动力学，并表明存在两个具有不同对称性的近简并连续共振，这两个共振都可以通过内部转换耦合到具有相同总对称性的离子对状态而衰减。
英文摘要：
We present a combined experimental and theoretical study on the photodissociation dynamics of ion-pair formation in O$_2$ following resonant two-photon absorption of a 9.3 eV femtosecond pulse, where the resulting O$^+$ ions are detected using 3-D momentum imaging. Ion-pair formation states of $^3Σ^-_g$ and $^3Π_g$ symmetry are accessed through predissociation of optically dark continuum Rydberg states converging to the B $^2Σ^-_g$ ionic state, which are resonantly populated via a mixture of both parallel-parallel and parallel-perpendicular two-photon transitions. This mixture is evident in the angular distribution of the dissociation relative to the light polarization, and varies with the kinetic energy release (KER) of the fragmenting ion-pair. The KER-dependent photoion angular distribution reveals the underlying two-photon absorption dynamics involved in the ion-pair production mechanism and indicates the existence of two nearly degenerate continuum resonances possessing different symmetries, which can both decay by coupling to ion-pair states of the same total symmetry through internal conversion.
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