Electron attachment to H2O in Ar, N2, and CH4 in electric field

Abstract

The attachment of electrons to H2O in Ar, N2 or CH4 is investigated using a parallel-plate drift-tube apparatus. Electrons are produced either by irradiation of the cathode with ArF laser photons or by two-photon-ionization of a trace of trimethylamine in a buffer gas. The transient voltage pulses induced by the electron motion between the electrodes are observed. The electron attachment rate of H2O is determined from the ratio of transient voltage with and without H2O added to the buffer gas. The measured electron attachment rate constants of H2O in Ar increase with E/N from 2 to 15 Td. Electron attachment due to the formation of ‘‘temporary’’ negative ions in the H2O–N2 and H2O–CH4 mixture were observed. The lifetime of the negative ion was determined to be about 200 ns, whose nature is discussed. The ‘‘apparent’’ electron attachment rate constants for the formation of ‘‘temporary’’ negative ions in the H2O–CH4 gas mixture are measured for E/N from 1 to 20 Td. The electron drift velocities for the gas mixtures of H2O in various buffer gases are measured.