Temperature dependences of rate coefficients for electron catalyzed mutual neutralization

Area of Science:

• Plasma Physics
• Chemical Kinetics
• Mass Spectrometry

Background:

• The flowing afterglow technique using variable electron and neutral density attachment mass spectrometry (VENDAMS) has provided evidence for electron catalyzed mutual neutralization (ECMN). This process involves the neutralization of positive and negative ions facilitated by an electron: A(+) + B(-) + e(-) → A + B + e(-).

Purpose of the Study:

• To measure the rate constants for ECMN involving specific polyatomic and diatomic anions with monatomic cations.
• To investigate the temperature dependence of ECMN rate constants.
• To compare ECMN rates for different anion and cation species.

Main Methods:

• Utilized the variable electron and neutral density attachment mass spectrometry (VENDAMS) flowing afterglow technique.
• Measured ECMN rate constants for POCl(3)(-), POCl(2)(-), and Br(2)(-) anions interacting with Ar(+) and Kr(+) cations.
• Conducted measurements over a temperature range of 300 K to 500 K.

Main Results:

• All measured ECMN rate constants exhibited a strong negative temperature dependence.
• No significant variation in rate constants was observed with different cation types (Ar(+) and Kr(+)).
• Polyatomic anions (POCl(3)(-) and POCl(2)(-)) showed measurably higher ECMN rate constants (~1 × 10(-18) cm(6) s(-1) at 300 K) compared to the diatomic anion Br(2)(-) [(5.5 ± 2) × 10(-19) cm(6) s(-1) at 300 K].

Conclusions:

• The observed negative temperature dependence supports ECMN as a three-body process involving two ions and an electron.
• The size and structure of the anion influence ECMN rates, with polyatomic anions reacting faster than diatomic ones.
• These findings contribute to understanding plasma charge loss mechanisms and chemical kinetics in ion-molecule reactions.