Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
J Chem Phys. 2011 Jul 28;135(4):044319. doi: 10.1063/1.3609110.
In molecular beams, the tertiary amine N,N-dimethylisopropyl amine can form molecular clusters that are evident in photoelectron and mass spectra obtained upon resonant multiphoton ionization via the 3p and 3s Rydberg states. By delaying the ionization pulse from the excitation pulse we follow, in time, the ultrafast energy relaxation dynamics of the 3p to 3s internal conversion and the ensuing cluster evaporation, proton transfer, and structural dynamics. While evaporation of the cluster occurs in the 3s Rydberg state, proton transfer dominates on the ion surface. The mass-spectrum shows protonated species that arise from a proton transfer from the alpha-carbon of the neutral parent molecule to the N-atom of its ionized partner in the dimer. DFT calculations support the proton transfer mechanism between tightly bonded cluster components. The photoelectron spectrum shows broad peaks, ascribed to molecular clusters, which have an instantaneous shift of about 0.5 eV toward lower binding energies. That shift is attributed to the charge redistribution associated with the induced dipoles in surrounding cluster molecules. A time-dependent shift that decreases the Rydberg electron binding energy by a further 0.4 eV arises from the structural reorganization of the cluster solvent molecules as they react to the sudden creation of a charge.
在分子束中，叔胺 N,N-二甲基异丙基胺可以形成分子簇，这些分子簇在通过 3p 和 3s 里德堡态的共振多光子电离获得的光电子和质谱中显而易见。通过延迟从我们跟随的激发脉冲的电离脉冲，我们实时跟踪 3p 到 3s 内转换的超快能量弛豫动力学以及随后的簇蒸发、质子转移和结构动力学。虽然簇的蒸发发生在 3s 里德堡态，但质子转移在离子表面占主导地位。质谱显示出质子化物种，这些物种是由中性母体分子的α-碳原子向其离子化伙伴的 N-原子转移质子产生的。DFT 计算支持紧密结合的簇组件之间的质子转移机制。光电子能谱显示出宽的峰，归因于分子簇，这些峰瞬时向更低的结合能移动约 0.5 eV。这种位移归因于与周围簇分子中诱导偶极子相关的电荷重新分布。由于簇溶剂分子对突然产生的电荷的反应，结构重组导致的另一个 0.4 eV 的里德堡电子结合能的时变位移。
