Resonance-enhanced two-photon ionization spectroscopy and theoretical calculations of 3,5-difluoroanisole and its Ar-containing complex

The structure and vibrations of 3,5-difluoroanisole (3,5-DFA) in the first electronically excited (S1) state were studied by mass-analyzed resonant two-photon ionization (R2PI) technique as well as the quantum chemical calculations. The ab initio and density functional theory (DFT) calculations reveal that only one structure is stable for each of the S0, S1, and D0 states. In the one color R2PI spectrum, the band origin of the S1 ← S0 electronic transition (00 band) of 3,5-DFA is found to be 37,595 ± 3 cm−1. In the S1 state, most of the bands observed are related to the in-plane ring deformation and out-of-plane bending vibrations. The adiabatic ionization energy (IE) of 3,5-DFA is determined to be 70,096 ± 15 cm−1 by the two color R2PI technique, in agreement with the values predicted by the DFT approaches. The dihalogen-substitution effects on the molecular structure, vibrational frequencies, and electronic transition and ionization energies were discussed in detail. The van der Waals complex of 3,5-DFA with argon (3,5-DFA···Ar) was also observed and studied. The 00 band of 3,5-DFA···Ar complex is red-shifted by about 9 cm−1 with respect to that of 3,5-DFA. Both the experimental data and the calculated results indicate that the formation of 3,5-DFA···Ar complex gives only a weak influence on the properties of 3,5-DFA moiety.

1C-R2PI spectrum of 3,5-difluoroanisole. The inset shows the band origin of its complex with one Ar atom.Figure optionsDownload as PowerPoint slideHighlights
► Resonant two-photon ionization spectrum of 3,5-difluoroanisole was firstly obtained.
► The S1 ← S0 electronic transition energy and the ionization energy were determined.
► Formation of Ar complex gives a weak influence on the properties of 3,5-DFA moiety.
► The calculated results compared well with the experimental results.
► The dihalogen-substitution effect was discussed in detail.