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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Threshold Photoelectron-Photoion Coincidence Spectroscopy of Perfluorocarbons. 2. Unsaturated and Cyclic Perfluorocarbons C_2F_4, C_3F_6, 2-F_4F_8, and c-C_4F_8
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Threshold Photoelectron-Photoion Coincidence Spectroscopy of Perfluorocarbons. 2. Unsaturated and Cyclic Perfluorocarbons C_2F_4, C_3F_6, 2-F_4F_8, and c-C_4F_8

机译：全氟化碳的阈值光电子-光子符合光谱。 2.不饱和和环状全氟化碳C_2F_4，C_3F_6、2-F_4F_8和c-C_4F_8

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Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy of three unsaturated ( C_2F_4, C_3F_6, 2-F_4F_8) and one cyclic (c-C_4F_8) perfluorocarbons has been performed using vacuum-ultraviolet radiation from a synchrotron source in the energy range 10-27 eV. Electrons and ions are detected by threshold electron analysis and time-of-flight mass spectrometry, respectively, allowing breakdown diagrams that show the formation probability of fragment/parent ions as a function of the internal energy of the parent ion to be obtained. Fixed-energy TPEPICO spectra with improved time resolution were performed on some of the fragment ions observed, from which the mean kinetic energy released in fragmentation was determined. High-resolution (ca. 0.01 eV at 10 eV) threshold photoelectron spectra of the three unsaturated species have been recorded, and assignments have been made of the type of electron removed by photoionization to the observed states of the parent ion. Unlike the saturated perfluorocarbons studied in the previous paper, the ground states of C_2F_4~+, C_3F_6~+, and 2-F_4F_8~+ are bound in the Franck-Condon region. The first photoelectron band of C_2F_4 and C_3F_6 shows vibrational structure associated with the v_2 C=C stretching mode. This suggests that upon ionization the C=C bond weakens. From the fragment ions observed by decay of excited states of these three parent ions, there is some correlation between the ions that are observed and the nature of the orbitals from which an electron has been removed. This observation indicates that decay from these states takes place impulsively, and many of these excited states are probably repulsive in the Franck-Condon region. From the c-C_4F_8 study we have determined a new onset of ionization for c-C_4F_8 (11.6 ± 0.2 eV) and a new upper limit for the heat of formation at 298 K of C_3F_5~+ (84 ± 20 kJ mol~(-1)).
机译：三种全不饱和碳（C_2F_4，C_3F_6、2-F_4F_8）和一个环状（c-C_4F_8）全氟化碳的阈值光电子重合（TPEPICO）光谱已使用来自同步加速器源的10-27 eV范围内的真空紫外辐射。通过阈值电子分析和飞行时间质谱分别检测电子和离子，从而获得分解图，该分解图显示碎片/母离子的形成概率随母离子内部能量的变化。对观察到的某些碎片离子进行了具有改进的时间分辨率的固定能量TPEPICO光谱，从中确定了碎片中释放的平均动能。记录了三种不饱和物质的高分辨率（在10 eV时约为0.01 eV）阈值光电子能谱，并已将通过光电离去除的电子类型分配给了观察到的母体离子状态。与之前的论文研究的饱和全氟化碳不同，C_2F_4〜+，C_3F_6〜+和2-F_4F_8〜+的基态在Franck-Condon区域内键合。 C_2F_4和C_3F_6的第一光电子带显示了与v_2 C = C拉伸模式相关的振动结构。这表明在电离时，C ＝ C键减弱。从通过这三个母离子的激发态衰减观察到的碎片离子中，观察到的离子与去除电子的轨道的性质之间存在一定的相关性。该观察结果表明，这些状态的衰减是冲动发生的，并且许多这些激发态在法兰克-康登地区很可能是排斥的。通过c-C_4F_8研究，我们确定了c-C_4F_8的新电离起点（11.6±0.2 eV）和298 K的C_3F_5〜+（84±20 kJ mol〜（- 1））。

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