Vacuum ultraviolet (VUV) photoionization and dissociative photoionization of NO2 in the 10.0-15.5 eV energy range have been investigated in detail by using high-resolution double imaging photoelectron photoion coincidence (i2PEPICO) at synchrotron SOLEIL. Five low-lying electronic states of the NO2+ cation, X1Σg+, a3B2, b3A2, A1A2 and B1B2, are prepared with well-resolved vibronic structures and their state-specific dissociation mechanisms are unraveled and discussed. The present experimental results clarify that except the X1Σg+ ground electronic state and the first three vibrational levels of the a3B2 electronic state, the other cationic states of NO2+ within the present energy range are totally dissociative towards the NO+(X1Σ+) + O(3P) and/or NO+(X1Σ+) + O(1D) dissociation limits. An energy barrier exists along the direct dissociation route of the a3B2 state, and the b3A2 electronic state is a quasi-bound state with a very shallow well, both of which adiabatically correlate to the NO+(X1Σ+) + O(3P) dissociation limit. The a3B2 state mainly with bending vibration excitations undergoes a non-adiabatic transition to the 23A''(3B1) repulsive state along its bending potential energy curve and then predissociates into the NO+(X1Σ+) + O(3P) products. Our experimental results firstly demonstrate that the NO+(X1Σ+, v) fragment ions produced from individual vibronic levels of the dissociative NO2+(a3B2, b3A2) states are produced at the v = 0 ground vibrational level with a high rotational population due to the excitation of the vibrational bending mode of NO2+ and the associated imparted torque upon dissociation. The slower predissociations of the A1A2 and B1B2 electronic states via their spin-orbit couplings with the repulsive 23A''(3B1) state produce the NO+(X1Σ+) and O(3P) fragments with a long vibrational progression. In addition, the B1B2 state can also undergo a radiationless transition such as internal conversion into the hot X1Σg+ state and then dissociate into the second dissociation channel correlated to the NO+(X1Σ+) and O(1D) products.

中文翻译：

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通过同步加速器双成像光电子光子重合，可在10.0-15.5 eV能量范围内实现NO2 +的高分辨率振动态特定解离。

通过在同步加速器SOLEIL上使用高分辨率双成像光电子光子重合（i2PEPICO），详细研究了在10.0-15.5 eV能量范围内的NO2的真空紫外（VUV）光电离和离解光电离。制备了具有良好解析的电子结构的NO2 +阳离子的五个低电子态X1Σg+，a3B2，b3A2，A1A2和B1B2，并阐明了它们的状态特异性解离机理。本实验结果表明，除了X1Σg+基态电子态和a3B2电子态的前三个振动能级外，在当前能级范围内，NO2 +的其他阳离子态都朝着NO +（X1Σ+）+ O（3P）完全分解和/或NO +（X1Σ+）+ O（1D）解离极限。在a3B2态的直接解离路径上存在能垒，b3A2电子态是具有非常浅的阱的准结合态，两者都绝热地与NO +（X1Σ+）+ O（3P）的解离极限相关。主要具有弯曲振动激发的a3B2状态沿其弯曲势能曲线经历非绝热转变为23A''（3B1）排斥状态，然后预分解为NO +（X1Σ+）+ O（3P）产物。我们的实验结果首先证明，由离解性NO2 +（a3B2，b3A2）态的各个振动能级产生的NO +（X1Σ+，v）碎片离子是在v = 0的地面振动能级下产生的，并且由于激发而具有高旋转种群解离时NO 2+的振动弯曲模式和相关的传递扭矩的关系。A1A2和B1B2电子态通过其自旋轨道耦合与排斥性23A''（3B1）状态的较慢的预离解产生具有长振动进程的NO +（X1Σ+）和O（3P）碎片。此外，B1B2状态还可以经历无辐射跃迁，例如内部转换为热X1Σg+状态，然后离解为与NO +（X1Σ+）和O（1D）产物相关的第二离解通道。