CROSS-SECTIONS FOR THE FORMATION OF S- IONS BY ELECTRON-IMPACT ON OCS

Cross-sections, appearance energies and peak energies at which S- ion intensities are maximal have been measured for electron attachment to OCS as a function of electron impact energy in the energy range 0-20 e V using a time-of-flight mass spectrometer in a crossed-beams collisio n geometry. Maximum intensities of formation of S - were observed at f our electron impact energies of 1.4, 4.7, 7.0, and 10.2 eV with an acc uracy to +/-0.25 eV. The cross-sections measured at these energies wer e 2.6 x 10(-17), 1.5 x 10(-19), 1.8 x 10(-19), and 0.4 x 10(-19) cm(2) respectively, with an uncertainty of about +/-15%. From appearance en ergies of various resonance processes for S- formation and by using th ermochemical data we have been able to identify various dissociative e lectron attachment channels of OCS. Cross-section values for three add itional dissociative channels for the formation of S- and time-of-flig ht spectra representing the kinetic energies of these ions are reporte d for the first time.