Science Institute, University of Iceland, Dunhagi 3, 107 Reykjavík, Iceland.
Phys Chem Chem Phys. 2018 Jun 27;20(25):17423-17433. doi: 10.1039/c8cp02350f.
The multiphoton dynamics of CH3Br were probed by Mass Resolved MultiPhoton Ionization (MR-MPI), Slice Imaging and Photoelectron Imaging in the two-photon excitation region of 66 000 to 80 000 cm-1. Slice images of the CH3+ and Br+ photoproducts of ten two-photon resonant transitions to np and nd Rydberg states of the parent molecule were recorded. CH3+ ions dominate the mass spectra. Kinetic energy release spectra (KERs) were derived from slice and photoelectron images and anisotropy parameters were extracted from the angular distributions of the ions to identify the processes and the dynamics involved. At all wavelengths we observe three-photon excitations, via the two-photon resonant transitions to molecular Rydberg states, forming metastable, superexcited (CH3Br#) states which dissociate to form CH3 Rydberg states (CH3**) along with Br/Br*. A correlation between the parent Rydberg states excited and CH3** formed is evident. For the three highest excitation energies used, the CH3Br# metastable states also generate high kinetic energy fragments of CH3(X) and Br/Br*. In addition for two out of these three wavelengths we also measure one-photon photolysis of CH3Br in the A band forming CH3(X) in various vibrational modes and bromine atoms in the ground (Br) and spin-orbit excited (Br*) states.
通过在 66000 到 80000cm-1 的双光子激发区域内采用质量分辨多光子电离（MR-MPI）、切片成像和光电子成像技术，研究了 CH3Br 的多光子动力学。记录了十个双光子共振跃迁到母体分子 np 和 nd 里德伯态的 CH3+ 和 Br+光产物的十张切片图像。CH3+离子在质谱中占主导地位。从切片和光电子图像中推导出了动能释放谱（KER），并从离子的角分布中提取了各向异性参数，以确定所涉及的过程和动力学。在所有波长下，我们都观察到三光子激发，通过双光子共振跃迁到分子里德伯态，形成亚稳态、超激发态（CH3Br#），它们沿着 Br/Br解离，形成 CH3 里德伯态（CH3）。激发的母体里德伯态与形成的 CH3**之间存在相关性。对于使用的三个最高激发能量，CH3Br#亚稳态也会生成 CH3(X) 和 Br/Br的高动能碎片。此外，对于这三个波长中的两个，我们还测量了 CH3Br 在 A 带中的单光子光解，形成了各种振动模式的 CH3(X)和基态（Br）和自旋轨道激发态（Br*）中的溴原子。
