Measurements of thermal electron attachment rate coefficients to molecules using an electron swarm technique

Abstract

An existing electron swarm apparatus has been redesigned and upgraded. In particular, the new design incorporates a novel planar radioactive foil to form an integral part of the drift tube, allowing us to overcome inherent problems present in our earlier system which used a cylindrical radioactive source. In addition to this, substantial upgrades have been made to improve the gating and amplification electronics and the data acquisition system. This has resulted in a much greater signal to noise ratio and improved accuracy. This paper describes the upgraded apparatus and its use in obtaining thermal (300 K) attachment rate coefficients to a number of molecules. The quality of the measurements and data are illustrated through the measurement of the thermal attachment rate coefficient for SF6 (kth(SF6) = (2.38 ±0.15 ) ×10 -7 cm3 s-1). Thermal electron attachment rate coefficients for four other molecules are presented, namely for two derivatives of SF6, SF5CF3 and SF5Cl, and two perfluorocarbons, c-C4F8 and 2-C4F8.