Studies of the First Electronically Excited State of 3-Fluoropyridine and Its Ionic Structure by Means of REMPI, Two-Photon MATI, One-Photon VUV-MATI Spectroscopy and Franck–Condon Analysis

Physical Chemistry Chemical Physics Pub Date: 2021-12-31 DOI: 10.1039/D1CP04636E

Abstract

3-Fluoropyridine (3-FP) has been investigated by means of two-photon resonance-enhanced multi photon ionization (REMPI), mass-analyzed threshold ionization (MATI) and one-photon vacuum-ultraviolet (VUV) MATI spectroscopy. The aim was the determination of the effect of m-fluorine substitution on the vibronic structure of the first electronically excited and ionic ground state. The S1 excitation energy has been determined to be 35?064 ± 2 cm?1 (4.3474 ± 0.0002 eV). Strong evidence of a distinct vibronic coupling via ν16b and ν[Wag.out.,16a] to one or both of the lowest 1ππ* states has been found, which results in a warped S1 minimum structure with C1 symmetry. The adiabatic ionization energy of the ionic ground state (14a′, nN-LP orbital) has been determined to be 76?579 ± 6 cm?1 (9.4946 ± 0.0007 eV), which is the first value reported for this state. The origin of the D1 state (4a′′, π-orbital) is located close by at 77?129 cm?1 (9.5628 eV). As a result of the D0–D1 vicinity, the ionic ground state is coupled to the D1 state via ν[Wag.out.,16a] and ν10a, which induces a twisted D0 geometry with C1 symmetry. Furthermore, for the first time two-photon and one-photon MATI spectra are presented together, which yield a much better understanding of the ionic vibronic structure in comparison to either of these experiments alone.

Graphical abstract: Studies of the First Electronically Excited State of 3-Fluoropyridine and Its Ionic Structure by Means of REMPI, Two-Photon MATI, One-Photon VUV-MATI Spectroscopy and Franck–Condon Analysis
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