Selective detection of O(1S) following electron impact dissociation of O2 and N2O using a XeO* conversion technique

Abstract

We have observed the metastable species O(1S0) following the dissociation of molecules by pulsed electron impact. A crossed beam apparatus was used to obtain time-of-flight spectra of the fragments. We have employed a novel detector which consists of a layer of freshly deposited Xe. O(1S0) atoms impinging on the surface quickly form XeO* excimers which rapidly decay (<1 μs) producing easily detected photons. Our present results indicate that this method is sensitive (with high quantum efficiency) solely to the 1S state of oxygen. Other metastables (such as 5S and 1D) and ground state oxygen atoms have not been detected. Low resolution optical spectra of the XeO emission reveal bands at 375, 550, and 725 nm. Time-of-flight and fragment kinetic energy spectra for both target gases at various electron impact energies are presented together with excitation functions from threshold to 1000 eV. These have been made absolute using a Bethe–Born calibration technique for N2O. O2 data are calibrated relative to N2O. Maximum cross sections for O(1S) production are 2.25×10−17 cm2 at 45 eV and 2.1×10−18 cm2 at 80 eV for N2O and O2 targets, respectively.