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Vacuum ultraviolet absorption spectra (250-105 nm, 5 1 1.8 eV) and near-threshold electron energy-loss spectra (0 e V I , , , ) have been recorded for dimethyl ether (l), diethyl ether (2), tetrahydrofuran (3), 1,Cdioxane (4) and 3,4-dihydropyran (5). For the saturated compounds 1-4 t h e low-lying electronically excited states are predominantly Rydberg in nature, selectively mixed with valence-excited states. Also, t h e lowest triplet state in each of the saturated molecules is within 0.5 eV of t h e 'n,3s state. The spectra of 5 resemble those of unsaturated hydrocarbons; its lowest triplet state (37r7r*) is ca. 4.2 eV.In this paper we report the results of studies on the electronic excitation of some simple ethers. As well as vacuum ultraviolet (VUV) absorption spectra obtained using synchrotron radiation, we have recorded, for the first time, near-threshold electron energy-loss (EEL) spectra for dimethyl ether, diethyl ether, tetrahydrofuran, 1,4-dioxane and 3,4-dihydropyran

Electron swarm characteristic energies (Dr/ mu , where Dr is the lateral diffusion coefficient and mu the mobility) have been measured in pure CF4 at 293 K, using the Townsend-Huxley method. For E/N values (the ratio of applied electric field to gas number density) less than 23 Td (1 Td=10-21 Vm2), dissociative attachment does not interfere with the measurements. For E/N values between 23 and 44 Td lower and upper limits to Dr/ mu have been evaluated using present measurements and published attachment coefficients. A Monte Carlo simulation of electron transport through CF4 has provided low-energy elastic and vibrationally inelastic cross sections which are consistent with measured swarm transport parameters.

Electron-impact excitation of methane, silane, tetrafluoromethane and tetrafluorosilane has been explored in a trapped-electron spectrometer. Extensive vibrational excitation of CF4 was observed with electrons of very low incident energies. There was some evidence of multiple vibrational excitation in SiH, also, but the results for this molecule were not totally unambiguous. Nearthreshold vibrational excitation of SiF, was masked by effects attributed to a large cross-section for elastic scattering. Some optically forbidden electronic states have been located and assignments suggested. Short-lived negative-ion states (resonances) affect electronic excitation of the lowest excited Rydberg state in SiH4,CF4 and SiF4 as well as negative-ion production.

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