Variable Electron and Neutral Density Attachment Mass Spectrometry: Temperature-Dependent Kinetics of Electron Attachment to PSCl3 and PSCl2 and Mutual Neutralization of PSCl2− and PSCl− with Ar+

Abstract

We describe the VENDAMS (variable electron and neutral density attachment mass spectrometry) technique to measure the rate constants of various processes occurring as primary, secondary, and higher order chemistry in a flowing afterglow at high charge densities over a temperature range of 300 to 550 K. In particular, we report measurements of rate constants of ion-ion mutual neutralization and electron attachment to radical species, processes which have proven difficult to study through other means. The product negative ion abundances from the addition of PSCl(3) to an Ar(+)/e(-) plasma have been measured as a function of initial electron densities between 1 × 10(8) and 4 × 10(10) cm(-3). Data at lower electron densities yield branching ratios of the primary electron attachment to PSCl(3); determination of the reactions and rate constants occurring at low electron densities then allows for determination of the greater number of reactions and rate constants contributing at higher electron densities. Reaction rate constants and branching ratios of electron attachment to PSCl(2) are reported; this is the first measurement of electron attachment to a radical as a function of temperature. The data show an unusual negative temperature dependence; however, a zero or even slightly positive dependence is within the uncertainty. Measured electron attachment rate constants are 1.4 × 10(-7), 1.1 × 10(-7), and 9.1 × 10(-8) ± 40% cm(3) s(-1) at 300, 400, and 550 K, respectively; the dominant product channel is PSCl + Cl(-) (95, 87, and 77% at 300, 400, and 550 K), and the minor channel is PSCl(-) + Cl. Ion-ion mutual neutralization rate constants of both PSCl(-) and PSCl(2)(-) with Ar(+) are reported over the investigated temperature range; rate constants at 300 K are 4.9 × 10(-8) ± 20% cm(3) s(-1) and 4.5 × 10(-8) ± 15% cm(3) s(-1) and show temperature dependences of T(-0.5±0.3) and T(-0.9±0.3), respectively.