Time-resolved photoelectron imaging is employed to investigate the relaxation dynamics of the lowest two excited electronic states S₁(ππ*) and S₂(π3s/πσ*) in 2,4-difluoroaniline (24DFA). As the S₁(ππ*) state is populated directly following 289 nm excitation, the population undergoes ultrafast intramolecular vibrational redistribution on a 540 fs time scale, followed by efficient intersystem crossing from S₁(ππ*) to the triplet state within 379 ps, and the subsequent slower deactivation process of the triplet state. For excitation to the S₂(π3s/πσ*) state at 238 nm, the population probably bifurcates into two decay channels. The dominant channel with 84 fs involves ultrafast internal conversion to the S₁(ππ*) state, from which it relaxes to the electronic ground state on a 116 ps time scale. The other appears to involve motion along the S₂(π3s/πσ*) potential energy surface. Our data also determine experimentally the electronic energies of S₂(π3s/πσ*), S₃(ππ*), and several Rydberg states in 24DFA.

中文翻译：

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飞秒时间分辨光电子成像揭示光激发的2,4-二氟苯胺中的电子弛豫动力学

时间分辨光电子成像用于研究最低的两个电子激发态的弛豫动力学š ₁（ππ *）和小号₂（π 3小号/ πσ *）在2,4-二氟苯胺（24DFA）。由于在289 nm激发后直接填充了S ₁（ππ *）状态，因此该种群在540 fs的时间尺度上经历了超快的分子内振动重新分布，然后从S ₁（ππ*）在379 ps内变为三重态，随后的三重态钝化过程更慢。激发到小号₂（π 3小号/ πσ *）状态在238处，人口可能分叉成两个衰变道。具有84 fs的主导通道涉及到S ₁（ππ *）状态的超快内部转换，从该状态通道以116 ps的时间尺度松弛到电子基态。其它出现沿着涉及运动š ₂（π 3小号/ πσ *）势能面。我们的数据还通过实验确定了小号₂（π 3小号/ πσ *），š ₃（ππ在24DFA *），和几个德堡态。