Vibrational spectrum of p-fluoroanisole in the first excited state (S1) and ab initio calculations

The vibronic structure of p-fluoroanisole in the first excited state (S1) has been investigated with mass selected resonance-enhanced two photon ionization spectroscopy. The band origin of S1 ← S0 transition of p-fluoroanisole is measured to be 35149 cm−1, which is red-shifted by 1234 cm−1 with respect to that of anisole. Combining with the ab initio calculations, the measured frequencies 397, 487, 559, 840 and 1150 cm−1 in the S1 state are assigned as the in-plane ring vibrational mode 9b, 6a, 6b, 1 and 9a, respectively. The optimized molecular geometries and vibrational frequencies of p-fluoroanisole in the ground state (S0) and cation ground state (D0) are also achieved from DFT calculations.