Reaction‐induced mass discrimination in XQQ instruments. Absolute cross‐sections for N + SF6 → N2 + SF (x=1–5)

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Abstract
Dynamically‐correct branching ratios can be measured in a XQQ tandem mass spectrometer (MS/MS) under single‐collision conditions when the key MS/MS parameters are properly selected to correct for reaction‐induced mass discrimination within the RF‐only quadrupole mass filter (Q2). The energy dependence of the cross‐section, σ(E), for the reaction N + SF6 → N2+SFx+ (x = 1–5) was measured in the NBS triple quadrupole (QQQ) tandem mass spectrometer. For P≃0.02–0.13 mTorr and E ≃ 5–60 eV (Lab) [the range of collision energies used for collisionally activated dissociation (CAD)], identical σ(E) were measured from both the rate of reactant ion decay and the rate of product ion formation. Therefore, these σ values are substantially free from kinetic interferences (i.e., no back reactions, no impurity reactions, no scattering losses, minimal fringing fields, no mass discrimination, well‐defined gas target, etc.). Moreover, there is probably no significant systematic error in our measurements of the absolute σ values for N + SF6 → N2+SF (x = 1–5) because the σ values we measured with this same technique for Ne +˙+ Ne → Ne+Ne+˙, Ar+˙ + Ar → Ar+Ar+˙, and Ar+˙+N2 → Ar+N agreed well with literature values obtained with several well‐established techniques.

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