The electronic state spectroscopy of pyrimidine C₄H₄N₂ has been investigated using both high resolution VUV photoabsorption in the energy range 3.7 to 10.8 eV (335 to 115 nm) and lower resolution electron energy loss in the range 2 to 15 eV. The low energy absorption band, assigned to the (π*) ← 7b₂(n_N) (1¹B₁ ← 1¹A₁) transition, at 3.85(4) eV and the vibrational progressions superimposed upon it have been observed for the first time, due to the availability of a high-resolution photon beam (0.075 nm), corresponding to 3 meV at the midpoint of the energy range studied. Vibronic coupling has been shown to play an important role dictating the nature of the observed excited states, especially for the lowest ¹B₁ state. The 2¹B₁ state is proposed to have its origin at 7.026 eV according to the vibrational excitation reported in this energy region (7.8–8.4 eV). New experimental evidence of 4¹A₁ state with a maximum cross section at 8.800 eV is supported by previous ab initio quantum chemical calculations. Rydberg series have been assigned converging to the three lowest ionisation energy limits, 9.32 eV (²B₂), 10.41 eV (²B₁) and 11.1 eV (²A₁ + ²A₂) with new members reported for the first time and classified according to the magnitude of the quantum defects (δ). Additionally, the absolute differential cross section for inelastic electron scattering has been measured for the most intense band from 6.9 to 7.8 eV assigned to ¹ππ* (3¹A₁ + 2¹B₂).

Ion-pair formation in gaseous nitromethane (CH₃NO₂) induced by electron transfer has been studied by investigating the products of collisions between fast potassium atoms and nitromethane molecules using a crossed molecular-beam technique. The negative ions formed in such collisions were analysed using time-of-flight mass spectroscopy. The six most dominant product anions are NO₂ ⁻, O ⁻, CH₃NO₂ ⁻, OH ⁻, CH₂NO₂ ⁻ and CNO ⁻. By using nitromethane-d₃ (CD₃NO₂), we found that previous mass 17 amu assignment to O ⁻ delayed fragment, is in the present experiment may be unambiguously assigned to OH ⁻. The formation of CH₂NO₂ ⁻ may be explained in terms of dissociative electron attachment to highly vibrationally excited molecules.

Ion-pair formation has been studied in hyperthermal (30–100 eV) neutral potassium collisions with gas phase thymine (C₅H₆N₂O₂) and uracil (C₄H₄N₂O₂). Negative ions formed by electron transfer from the alkali atom to the target molecule were analysed by time-of-flight (TOF) mass spectrometry. The most abundant product anions are assigned to CNO⁻ and (U–H)⁻/(T–H)⁻ and the associated electron transfer mechanisms are discussed. Special emphasis is given to the enhancement of ring breaking pathways in the present experiments, notably CNO⁻ formation, compared with free electron attachment measurements.

The first ab initio calculations of the vertical excitation energies and oscillator strengths are presented for the neutral electronic transitions of methyl formate, C₂H₄O₂. The highest resolution VUV photoabsorption spectrum of the molecule yet reported is presented over the wavelength range 115 to 310 nm (10.8 to 4.0 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new theoretical results. The calculations have been carried out to determine the excitation energies of the lowest energy ionic states of methyl formate and are compared with a newly recorded He(I) photoelectron spectrum (10.4 to 17.0 eV). New vibrational structure is observed in the first photoelectron band. The photoabsorption cross-sections have been used to calculate the photolysis lifetime of methyl formate in the upper stratosphere (20–50 km).