Direct Experimental Evidence for Dissociative Photoionization of Oxygen Molecule via 2危u鈥?/sup> Ionic 鈥淥ptical Dark鈥?State

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• 作者：Xiaofeng Tang ; Xiaoguo Zhou ; Manman Wu ; Yu Cai ; Shilin Liu ; Liusi Sheng
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：September 27, 2012
• 年：2012
• 卷：116
• 期：38
• 页码：9459-9465
• 全文大小：316K
• 年卷期：v.116,no.38(September 27, 2012)
• ISSN：1520-5215

文摘

Direct experimental evidence for dissociative photoionization of oxygen molecule via the ²危_u^{鈥?/sup> ionic optical dark state is presented by an investigation using the method of threshold photoelectron鈥損hotoion coincidence (TPEPICO) velocity imaging. Besides vibrational progress of the B2危_g鈥?/sup> state, several weak vibrational bands of the 2危_u鈥?/sup> ionic optical dark state are observed concomitantly in an excitation energy range of 20.2鈥?1.1 eV. Only O+ fragments are detected in the whole excitation energy range; therefore, all vibrational bands are completely predissociative. TPEPICO three-dimensional time-sliced velocity images of O+ fragments dissociated from vibrational state-selected O₂+(2危_u鈥?/sup>,v+) ions are recorded. For the 2危_u鈥?/sup>(v+=0鈥?) vibrational states, only the lowest dissociation channel of O+(4S) + O(3P) is observed. Once the photon energy is slightly increased to the 2危_u鈥?/sup>(v+=4) level, a new concentric doughnut appears in the image, indicating that the second dissociation channel of O+(4S) + O(1D) is identified indeed. With the aid of potential energy curves, the dissociative mechanism of O₂+ in the 2危_u鈥?/sup>(v+) state is proposed.}