Emission Spectra of Benzene, Toluene, and Xylenes by Controlled Electron Impact

Abstract

Abstract The emission spectra of gaseous aromatic hydrocarbons under electron impact excitation (60–300 eV) were measured in the 220–450 nm region at very low pressures. A characteristic band was observed in all cases in the 240–340 nm region; this band was assigned to the transition from the lowest excited singlet state to the electronic ground state. Photoemissions from the fragment species, such as H (Balmer series) and CH (A→X, B→X), were also observed. The excited species were concluded, from the relations of the emission intensities to the electron-beam current and to the gas pressure, to be produced by one-electron processes. The relative intensity and the vibrational structure of the observed spectra were examined and compared with those of the fluorescence spectra produced by photo-excitation.