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Ultrafast Imaging of Electronic Relaxation in Ortho-xylene: New Features from Fragmentation-Ion Spectroscopy 下载免费PDF全文
After light absorption, a molecule can undergo ra- diationless processes, and photophysics is one of the important general types. The photophysical pro- cesses involve internal conversion (IC) due to elec- tronic nonadiabaticity and intersystem crossing (ISC) induced by spin-orbit coupling. In polyatomic molecules that are excited IC and ISC to vibronic to higher electronic states, levels of lower electronic states are two dominant mechanisms. With the ad- vent of femtosecond ultrashort pulse, tracking and controlling the ultrafast photophysical processes be- come realizable. Due to the fact that ISC requires a change in the spin of an electron, it is usually a slower process than IC. However, extensive reports show that ultrafast competing ISC exists in a number of systems. Re- cently, Richter et al. reported femtosecond ISC in cytosine. Martinez-Fernandez et al. simulated the deactivation dynamics of photo-excited 6-thioguanine using a direct surface hopping dynamics approach Their simulations show that 6-thioguanine is another example of a system showing ultrafast ISC that can compete with IC in the same time scale. Both the spin-orbit and the dynamic couplings are important to describe realistically the excited state dynamics of 6-thioguanine. A similar phenomenon has also been evidenced in the S1 state of benzene. The exper- imental results show that the ultrafast decay of the S1 state is due to competing IC and ISC processes and both processes occur on a femtosecond timescale. Spin-orbit coupling is highly effective when the in- volved states are nearly isoenergetic. 相似文献
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通过半导体激光照射采样气体,利用光电检测电路检测前向散射光强,并通过滤波电路、真值转换电路以及后置放大电路,最终将信号进行采样送入微处理器中处理。通过对信号处理电路的各个模块进行动态特性分析,从而找出对系统影响最大的模块部分并提出改进。结果表明,光电检测电路的动态特性对系统的影响最为显著,通过适当减小负载电阻,可有效改善电路的线性动态范围。 相似文献
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构建了一套光谱测量系统,以太阳光为光源,利用高精度成像光谱仪采集太阳光谱,选取某一时刻的太阳光谱为参考,结合当时的污染气体浓度数据,应用差分吸收原理,反演出其他任意时刻的NO2浓度。运用Origin7.5软件进行光谱解析,根据HITRAN数据库绘制吸收截面谱,并获取指定数值的应用,实现了对光谱谱线的定量分析,并且误差小。该反演过程具有光谱处理失真低以及反演参量精度高的特点,一定程度上提高了太阳光谱反演气体浓度的精度。实验结果与其他设备测量结果一致,证实了该方法的可行性。 相似文献
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为了满足数字摄像法能见度测量仪均匀光源的要求,提高半导体发光二极管照明的均匀性,该文提出一种基于数字图像分析技术的设计方法。首先测量单颗LED在模组区域的亮度分布,进而拟合分布函数,再运用多颗LED亮度叠加原理,计算出不均匀度最小的多颗LED阵列方式,或固定均匀度对应的最佳尺寸。对仿真数据和实测数据进行对比分析,结果表明,该文计算出的LED阵列方式,与单边阵列相比,均匀度显著提高,最高可达95%以上。 相似文献
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为了研究探测光波长的漂移对能见度测量的影响。从Koschmieder经验公式的定义出发,根据实验测得400 nm~1 100 nm波段的气溶胶透过率,分析研究探测光波长漂移对能见度测量结果的影响。结果表明,能见度测量的相对误差与探测光波长和波长的漂移范围以及气溶胶消光特性有关,能见度测量的相对误差随着探测光的波长漂移范围线性增大,随着波长漂移范围的增大,各个波长的能见度测量相对误差线性增大的速率不同,对于相同的波长漂移范围,使用不同的探测光波长产生的能见度测量相对误差不同。对于某一大气环境,使用特定的波长而且中心波长稳定的光作为探测光可以明显减小由于探测光波长漂移引起的能见度测量相对误差。 相似文献