Ion-Molecule Reactions of Vibrationally State-Selected NO+ with Small Alkyl Halides

Article abstract of DOI:10.1021/j100201a042

The effects of vibrational excitation in NO⁺ (v=0-5) on its reactivity with small alkyl halides (C_nH_2n+1X; n=1-3; X=Cl, Br, I) have been investigated under thermal translational conditions.The method combines resonance enhanced multiphoton ionization to form state-selected NO⁺(v), and Fourier transform in cyclotron resonance techniques to trap, react, and detect ions.Besides vibrational quenching of NO⁺(v > 0), which is found to be very efficient with alkyl halides, three reaction channels are observed: charge transfer, halide transfer, and C_nH_2nNO⁺ formation.Branching ratios and rate constants have been determined for the different channels as a function of the NO⁺(v=0) vibrationally energy.Endoergic charge transfer is efficiently driven by vibrational excitation.Halide transfer is the major channel if it is significantly exothermic for NO⁺(v=0).If this is not the case, adding vibrational energy in NO⁺(v=0) is only marginally effective in driving this channel.The data suggest that rearrangements in NO⁺-alkyl halide reaction intermediates and in carbonium ions are very rapid.The C_nH_2nNO⁺ formation channel is only observed with n-propyl and isopropyl chloride where it is dominant for NO⁺(v=0).Increasing vibrational excitation inhibits C3H6NO⁺ formation.The results are discussed in terms of possible reaction mechanisms.