Physique des Interactions Ioniques et Moleculaires, UMR CNRS 7345, Aix-Marseille Université, Avenue Escadrille Normandie-Niémen, 13397 Marseille Cedex 20, France.
Institut des Sciences Moléculaires d'Orsay, CNRS UMR 8214, Université Paris Sud 11, 91405 Orsay Cedex, France.
J Chem Phys. 2014 Jan 14;140(2):024302. doi: 10.1063/1.4858409.
The electronic spectra of cold benzylium (C6H5-CH2 (+)) and 1-phenylethyl (C6H5-CH-CH3 (+)) cations have been recorded via photofragment spectroscopy. Benzylium and 1-phenylethyl cations produced from electrosprayed benzylamine and phenylethylamine solutions, respectively, were stored in a cryogenically cooled quadrupole ion trap and photodissociated by an OPO laser, scanned in parts of the UV and visible regions (600-225 nm). The electronic states and active vibrational modes of the benzylium and 1-phenylethyl cations as well as those of their tropylium or methyl tropylium isomers have been calculated with ab initio methods for comparison with the spectra observed. Sharp vibrational progressions are observed in the visible region while the absorption features are much broader in the UV. The visible spectrum of the benzylium cation is similar to that obtained in an argon tagging experiment [V. Dryza, N. Chalyavi, J. A. Sanelli, and E. J. Bieske, J. Chem. Phys. 137, 204304 (2012)], with an additional splitting assigned to Fermi resonances. The visible spectrum of the 1-phenylethyl cation also shows vibrational progressions. For both cations, the second electronic transition is observed in the UV, around 33,000 cm(-1) (4.1 eV) and shows a broadened vibrational progression. In both cases the S2 optimized geometry is non-planar. The third electronic transition observed around 40,000 cm(-1) (5.0 eV) is even broader with no apparent vibrational structures, which is indicative of either a fast non-radiative process or a very large change in geometry between the excited and the ground states. The oscillator strengths calculated for tropylium and methyl tropylium are weak. Therefore, these isomeric structures are most likely not responsible for these absorption features. Finally, the fragmentation pattern changes in the second and third electronic states: C2H2 loss becomes predominant at higher excitation energies, for both cations.
已通过光碎片光谱记录了冷苯甲鎓（C6H5-CH2 (+)）和 1-苯乙基（C6H5-CH-CH3 (+））阳离子的电子光谱。分别从电喷雾苯甲胺和苯乙胺溶液中产生的苯甲鎓和 1-苯乙基阳离子被储存在低温四极离子阱中，并通过 OPO 激光光解，在 UV 和可见区域（600-225nm）中扫描。通过从头算方法计算了苯甲鎓和 1-苯乙基阳离子的电子态和活性振动模式，以及它们的薁鎓或甲基薁鎓异构体的电子态和活性振动模式，以便与观察到的光谱进行比较。在可见区域观察到尖锐的振动进展，而在 UV 区域吸收特征则宽得多。苯甲鎓阳离子的可见光谱与氩标记实验中获得的光谱相似[V. Dryza、N. Chalyavi、J. A. Sanelli 和 E. J. Bieske，J. Chem. Phys. 137, 204304 (2012)]，另外分配给费米共振。1-苯乙基阳离子的可见光谱也显示出振动进展。对于这两种阳离子，第二电子跃迁在 UV 中观察到，约 33000cm(-1)（4.1eV），并显示出拓宽的振动进展。在这两种情况下，S2 优化的几何形状是非平面的。在约 40000cm(-1)（5.0eV）处观察到的第三个电子跃迁甚至更宽，没有明显的振动结构，这表明要么是快速的非辐射过程，要么是在激发态和基态之间的几何形状发生了非常大的变化。薁鎓和甲基薁鎓的计算振子强度较弱。因此，这些异构体结构不太可能是这些吸收特征的原因。最后，在第二和第三电子态下，碎片模式发生变化：对于两种阳离子，在较高的激发能下，C2H2 损失变得占主导地位。
