Isotope effect in cross-section of (M−H/D)− negative ions formation from CF3COOH and CF3COOD

• Electron attachment by trifluoroacetic acid and its deuterated analog was studied.
• The isotope effect in cross-sections negative ions formation was measured.
• The largest isotope effect was found for (M−H/D)− ions.
• The hydrogen/deuterium atom loss is explained by tunneling predissociation mechanism.

In the present paper the processes of resonant electron attachment by trifluoroacetic acid molecules (CF3COOH) and its deuterated analog (CF3COOD) leading to formation of fragment negative ions have been investigated by negative ion mass spectrometry. Inverse or small direct isotope effect was detected for majority of negative ions. It is expressed both in difference between cross-section of ion formation, and in resonance peak displacement over energy scale for isotopically substituted ions from CF3COOH and CF3COOD. Isotope effect of maximal magnitude σ(H)/σ(D) ≈ 19 was registered for (M−H/D)− ions at electron energy 0.73 eV, and formation of these ions was explained by the mechanism of tunneling predissociation.

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