Excited states of isoxazole molecules studied by electron energy-loss spectroscopy

Abstract

Electron energy-loss spectra were measured in isoxazole in the excitation energy range 3.5−10 eV to investigate the valence excited states. Spectra recorded at different scattering conditions enabled the identification of the singlet and triplet states and the determination of their vertical excitation energies. The two lowest energy triplet bands, ππ* 13A' and ππ* 23A' at 4.20 and 5.30 eV, respectively show vibrational progressions. The first triplet state, 15a'π* 13A” that involves excitation from the nitrogen lone-pair orbital is observed at 5.68 eV. The three singlet valence states, ππ* 11A', nNπ* 11A” and ππ* 21A' are observed at 5.96, 6.49 and 6.88 eV, respectively in accord with the absorption measurements. Resonance excitation of the triplet and singlet states was noticed.