Abstract
The resonance-enhanced two-photon ionization (R2PI) and mass-analyzed threshold ionization (MATI) spectra of 3-fluoro-5-methylanisole (3F5MA) were recorded to explore the conformers arising from the rotation of meta-methyl group (m-CH3) and methoxy group (OCH3), namely the staggered (s)/eclipsed (e)-cis/trans 3F5MA. The theoretical calculations predicted that the stable conformer of cis 3F5MA is staggered in the S0 and S1 states, but eclipsed in the D0 state. While for trans 3F5MA, the staggered conformer is stable only in the S1 state and the eclipsed one is stable in the S0 and D0 states. The first electronic excitation energies (E1s) of cis and trans 3F5MA were determined to be 36,709 ± 3 and 36,615 ± 3 cm-1 by the R2PI spectroscopy. Correspondingly, by the MATI spectroscopy, the adiabatic ionization energies (IEs) were measured to be 66,908 ± 5 and 66,692 ± 5 cm-1. Compared with the cis 3F5MA, more low-frequency vibronic bands assigned to m-CH3 torsions are observed for the trans conformer in the R2PI spectrum, supporting the theoretically predicated e-trans → s-trans isomerization upon excitation. The MATI spectra of the cis and trans conformers are similar. Most of the observed cationic bands are related to the m-CH3 tors...Continue Reading
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