Zhou Yiyong, Meng Qingnan, Mo Yuxiang
Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084, China.
J Chem Phys. 2014 Jul 7;141(1):014301. doi: 10.1063/1.4884906.
The photodissociation dynamics of O2, O2 + hυ → O((3)P) + O(2p(3)((4)S)3s, (3)S/(5)S), has been studied by combining the XUV laser pump / UV laser probe and velocity map imaging methods in the photon energy range 14.64-15.20 eV. The fragment yield spectra of O((3)S) and O((5)S) and their velocity map images have been recorded using the state-selective (1+1) REMPI method to detect the fragments. The fragment yield spectra show resolved fine structure that arises from the predissociated Rydberg states I, I' and I″ ((3)Π(Ω = 0,1,2)). The branching ratios between the two decay channels have been measured by one-photon ionization of the fragments O((3)S) and O((5)S) simultaneously. It is surprising to find that the dissociation cross sections for the production of O((5)S) are larger than, or comparable to, those of O((3)S) for the I and I' states, while the cross sections for the production of O((5)S) are smaller than those of O((3)S) for the I″ state. All fragments O((5)S) arise from perpendicular transitions, which provides direct experimental evidence about the symmetry assignments of the states I, I' and I″ excited in this energy region. Although most of the fragments O((3)S) arise from perpendicular transitions, some of them are from parallel transitions. Based on the calculated ab initio potential energy curves, we propose that the neutral dissociation into O((3)P) + O((3)S) occurs mainly via the interaction of the Rydberg states I, I', and I″ with the vibrational continuum of the diabatic 8(3)Π(u) state (1π(u)⁻¹(a⁴Π(u))3sσ(g), ³Π(u)), while the neutral dissociation into O((3)P) + O((5)S) occurs mainly via the interaction of Rydberg states I, I', and I″ with the diabatic 7(3)Π(u) (1π(g)⁻¹(X²Π(g))3pσ(u), ³Π(u)).
通过结合极紫外激光泵浦/紫外激光探测和速度成像方法，在14.64 - 15.20 eV的光子能量范围内研究了O₂的光解离动力学，即O₂ + hυ → O((³P)) + O(2p³((⁴S)3s, (³S)/(⁵S))。利用态选择(1 + 1)共振增强多光子电离方法探测碎片，记录了O((³S))和O((⁵S))的碎片产率谱及其速度成像图。碎片产率谱显示出由预解离的里德堡态I、I'和I″((³Π(Ω = 0,1,2)))产生的分辨精细结构。通过同时对碎片O((³S))和O((⁵S))进行单光子电离，测量了两个衰变通道之间的分支比。令人惊讶的是，发现对于I和I'态，产生O((⁵S))的解离截面大于或与产生O((³S))的解离截面相当，而对于I″态，产生O((⁵S))的截面小于产生O((³S))的截面。所有O((⁵S))碎片都来自垂直跃迁，这为该能量区域激发的态I、I'和I″的对称性归属提供了直接实验证据。虽然大多数O((³S))碎片来自垂直跃迁，但其中一些来自平行跃迁。基于从头计算的势能曲线，我们提出中性解离为O((³P)) + O((³S))主要通过里德堡态I、I'和I″与非绝热8(³Π(u))态(1π(u)⁻¹(a⁴Π(u))3sσ(g), ³Π(u))的振动连续体相互作用发生，而中性解离为O((³P)) + O((⁵S))主要通过里德堡态I、I'和I″与非绝热7(³Π(u)) (1π(g)⁻¹(X²Π(g))3pσ(u), ³Π(u))相互作用发生。
