EXCITED STATES OF NUCLEIC ACID BASES

原子核低激发态的位置、身份和寿命 酸碱将通过结合激光光电离和 激光光电子能谱与喷射，这使得超音速 非挥发性和热不稳定化合物的膨胀。 都是单色的 和双色电离方案，涉及泵浦之间的各种时间延迟 和探测激光器，将用于测量光谱和寿命的 激发态 问题的性质（nPi或PiPi）的最低 激发单重态的数量，以及低位PiPi态的数量等。 通过分析比较光电离和光电子 光谱，如我们最近对异喹啉的实验所示。 的 状态分配（在裸露和未取代的碱基中）可以通过以下方式来辅助： 研究甲基取代和氢键的光谱结果 (with醇和水），已知其相对于水蓝移nPI*。 PiPi* 表示。 讨论了氢键对光谱的影响 对理解核酸的电子结构很重要 碱在生物学上更相关的条件下的水溶液。 最后，研究了最低激发单重态的变化 (S1)寿命与能级处置在不同的基地，并与 甲基取代和氢键，将进行以获得 关于超快内部可能起源的信息 这些分子的转化。 这些实验的结果可以导致 更好地理解核酸的光谱学和生物物理学 基地仍然不完整和支离破碎。

The location, identity, and lifetime of low-lying excited states of nucleic acid bases will be investigated by combining laser photoionization and laser photoelectron spectroscopy with a spray-jet, which allows supersonic expansion of nonvolatile and thermally labile compounds. Both one-color and two-color ionization schemes, involving various time delay between pump and probe lasers, will be used to measure the spectra and lifetimes of the excited states. The question of the nature (nPi or PiPi) of the lowest excited singlet state, and the number of low-lying PiPi states, etc. can be probed by analyzing, and comparing, the photoionization and photoelectron spectra, as demonstrated by our recent experiments on isoquinoline. The state assignments (in bare and unsubstituted bases) can be aided by studying spectral consequences of methyl substitution and hydrogen bonding (with alcohol and water), which are known to blue shift nPI* relative to PiPi* states. The effects of hydrogen bonding on the spectra are also important for the understanding of electronic structure of nucleic acid bases in biologically more relevant conditions of aqueous solutions. Finally, the study of the variation of the lowest-excited-singlet-state (S1) lifetimes with energylevel dispositions in different bases, and with methyl substitution and hydrogen bonding, will be carried out to obtain information concerning the possible origin of the ultrafast internal conversion in these molecules. The results of these experiments can lead to better understanding of spectroscopy and photophysics of nucleic acid bases, which remain incomplete and fragmented.