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.

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 -fluorine substitution on the vibronic structure of the first electronically excited and ionic ground state. The S excitation energy has been determined to be 35 064 ± 2 cm (4.3474 ± 0.0002 eV). Strong evidence of a distinct vibronic coupling ν and ν to one or both of the lowest ππ* states has been found, which results in a warped S minimum structure with symmetry. The adiabatic ionization energy of the ionic ground state (14a', orbital) has been determined to be 76 579 ± 6 cm (9.4946 ± 0.0007 eV), which is the first value reported for this state. The origin of the D state (4a'', π-orbital) is located close by at 77 129 cm (9.5628 eV). As a result of the D-D vicinity, the ionic ground state is coupled to the D state ν and ν, which induces a twisted D geometry with 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.