Department of Physics, University of Gothenburg, 41296 Gothenburg, Sweden.
J Chem Phys. 2013 Aug 7;139(5):054306. doi: 10.1063/1.4817196.
Photon induced decay of C5(-) has been measured in an electrostatic storage ring. The time dependence of the photo-enhanced decay is close to a 1∕t decay which indicates a thermal process. The deviation from the expected power of -1 is quantitatively explained by the small heat capacity of the anion. Measurements of the photo-enhanced decay at different storage times and photon energies allow a determination of the radiative cooling rate and the energy distribution of the ions. The average energy content between 15 and 70 ms is found to vary as time to the power -0.72, and at 50 ms the ions contain an average excitation energy of 0.5 eV. The time dependent energy distribution is consistent with cooling by infrared photon emission if published oscillator strengths are reduced by a factor 2.5, in contrast to cooling of larger molecular carbon-based ions where electronic transitions cause a much stronger cooling.
在静电存储环中测量了 C5(-) 的光诱导衰减。光增强衰减的时间依赖性接近于 1∕t 衰减，表明这是一个热过程。由于阴离子的热容很小，因此可以定量解释与预期的 -1 次方功率的偏差。在不同的存储时间和光子能量下测量光增强衰减，可确定辐射冷却速率和离子的能量分布。在 15 到 70 毫秒之间的平均能量含量随时间的变化呈 -0.72 次方，在 50 毫秒时，离子的平均激发能为 0.5 eV。如果将发表的振子强度降低 2.5 倍，则时间相关的能量分布与红外光子发射冷却一致，而对于较大的基于碳的分子离子的冷却，电子跃迁会导致更强的冷却。
