Intramolecular charge transfer and the associated changes in molecular structure in N,N′-dimethylpiperazine are tracked using femtosecond gas-phase X-ray scattering. The molecules are optically excited to the 3p state at 200 nm. Following rapid relaxation to the 3s state, distinct charge-localized and charge-delocalized species related by charge transfer are observed. The experiment determines the molecular structure of the two species, with the redistribution of electron density accounted for by a scattering correction factor. The initially dominant charge-localized state has a weakened carbon–carbon bond and reorients one methyl group compared with the ground state. Subsequent charge transfer to the charge-delocalized state elongates the carbon–carbon bond further, creating an extended 1.634 Å bond, and also reorients the second methyl group. At the same time, the bond lengths between the nitrogen and the ring-carbon atoms contract from an average of 1.505 to 1.465 Å. The experiment determines the overall charge transfer time constant for approaching the equilibrium between charge-localized and charge-delocalized species to 3.0 ps.

使用飞秒气相 X 射线散射跟踪 N,N'-二甲基哌嗪的分子内电荷转移和分子结构的相关变化。分子在 200 nm 处被光激发至 3p 态。快速弛豫到 3s 状态后，观察到与电荷转移相关的不同电荷局域和电荷离域物种。该实验确定了两种物质的分子结构，并通过散射校正因子解释了电子密度的重新分布。最初占主导地位的电荷局域态的碳-碳键较弱，并且与基态相比，一个甲基重新定向。随后的电荷转移到电荷离域状态进一步拉长了碳-碳键，形成了延伸的 1.634 Å 键，并且还重新定向了第二个甲基。同时，氮和环碳原子之间的键长从平均 1.505 缩短至 1.465 Å。该实验确定了使电荷局域和电荷离域物质之间达到平衡的总电荷转移时间常数为 3.0 ps。