Methoxyl radical fluorescence in the electron impact excitation of dimethylether and related compounds

Electron impact excitation of dimethylether, dimethoxymethane and methyl formate at energies above ca. 8 eV leads to production of electronically excited methoxyl radicals, which fluoresce in the 300-450 nm region. Optical emission excitation functions for these methoxyl radicals have been measured. The threshold energy for production of excited methoxyl from dimethylether is 8.4 ± 0.4 eV. At energies only a little above threshold optically forbidden excitation processes are largely responsible for production of the excited methoxyl radicals, whereas at energies above 20 eV optically allowed processes dominate the excitation. In the case of dimethylether, non-linear pressure effects in the energy region close to threshold indicate that a triplet state is produced which may be capable of undergoing collisionally assisted predissociation at mTorr pressures.