VUV Study of Electron-Pyrimidine Dissociative Excitation

A crossed electron-gas beam system coupled to a VUV spectrometer has been used to investigate the dissociation of pyrimidine (C$_{4}$H$_{4}$N$_{2})$ into excited atomic fragments in the electron-impact energy range from threshold to 375 eV. Data have been made absolute using Lyman-$\alpha $ from H$_{2}$ as a secondary standard. The main features in the spectrum are the H Lyman series lines. The emission cross section of Lyman-$\alpha $ is measured to be (2.44 $\pm$ 0.25) 10$^{-18}$ cm$^{2}$ at 100 eV impact energy. The probability of extracting C or N atoms from the ring is shown to be very small. Possible dissociation channels and excitation mechanisms in the parent molecule will be discussed.