Resonant two-photon ionization spectroscopy of the 35Cl and 37Cl isotopomers of cis and trans 3-chloro-4-fluoroanisole

The effects of conformation and isotopic substitution on the properties of 3-chloro-4-fluoroanisole (3C4FA) were studied by mass-analyzed resonant two-photon ionization (R2PI) technique and theoretical calculations. In the one color R2PI spectra, the band origins of the S1 ← S0 electronic transitions (00 bands) of cis 35Cl–3C4FA and cis 37Cl–3C4FA were found to be equivalent at 34,703 ± 3 cm−1, while the 00 bands of trans 35Cl–3C4FA and trans 37Cl–3C4FA were found to be equivalent at 34,747 ± 3 cm−1. Assignments of the observed vibrational bands of R2PI spectra were made mainly based on the 10-electron, 8-orbital CASSCF/6-31g calculations and on conformity with the available data of the similar aromatic molecules in the literature. With the two color R2PI technique, the adiabatic ionization energies (IEs) of cis 35Cl–3C4FA and cis 37Cl–3C4FA were determined to be equivalently 67,349 ± 15 cm−1, while the IEs of trans 35Cl–3C4FA and trans 37Cl–3C4FA were determined to be equivalently 67,595 ± 15 cm−1. The conformational effect on the transition energies, ionization energies and vibrational frequencies of 3C4FA is greater than the isotopic effect. The hetero-dihalogen-substitution effect on the transition energies is also discussed.