| Summary: | 博士 === 國立臺灣大學 === 化學研究所 === 106 === Two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy was applied to study the vibrationally resolved cation spectra of structural isomers of 2-fluorostyrene and 3-fluorostyrene; 4-chloro-2-fluoroanisole; 3-chloro-5-fluoroaniline;sandwich organometallics incusing bis(η6-biphenyl)chromium ((η6-Ph2)2Cr), (η6-biphenyl)(η6-methylphenyl)chromium ((η6-Ph2)(η6-PhMe)Cr) and (η7-cycloheptatrienyl)(η5-cyclopentadienyl)chromium ((η7-C7H7)(η5-C5H5)Cr). The S1←S0 electronic transition and the adiabatic ionization energies of these molecular species have been precisely measured. Along with this, we performed ab initio and density functional theory calculations to predict the molecular structure, vibration, and electronic transition and ionization energies to support our experimental findings. Moreover, we compare these experimental findings with respective similar molecular species to gain knowledge about molecular properties.
Because of stereo effect, both experimental data and theoretical calculation results show that only the trans form of 2-fluorostyrene and 4-chloro-2fluorostyrene involve in the excitation and ionization processes. On the contrary, two stable species of 3-fluorostyrene were observed in the experiment. They were confirmed to be the cis and trans rotational isomers (rotamers) by our quantum chemical calculations.
By comparing all the experiments of aromatic molecules performed by our group in the past, one can find that the adiabatic energies of structural isomers follow the order: meta-＞ ortho-＞ para-, which we called “MOP rule.” Besides, our experimental data shows that there may exist an “additivity rule” associated with the energy shift resulting from the additional fluorine or chlorine substituents. By using these rules, we can reasonably predict the electronic transitional energy and ionization energy, which and speed up our laser spectroscopic experiments.
In addition, we have also recorded the spectra of some sandwich organometallics. These spectroscopic data are very rare in the literature. Possible reasons are as follows. The sandwich organometallic compounds are hard to be synthesized. Because they can decompose quickly in the atmosphere, the experiments should be performed in an oxygen-free environment. To gain enough vapors and to avoid clogging in the molecular beam valve, we designed a special pulsed molecular valve. With this valve, we succeeded in recording the vibronic, PIE, and MATI spectra of (η6-Ph2)2Cr and (η6-Ph2)(η6-PhMe)Cr. These new spectra are very helpful for us to learn photophysics of these sandwich organometallic molecules.
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