Vibrationally resolved transition state spectroscopy of the F + H2 and F + CH4 reactions

Abstract

The transition state regions of the F + para-H₂, F + normal-H₂, F + CH₄ and F + CD₄ reactions have been studied by slow electron velocity-map imaging (SEVI) spectroscopy of the anionic precursor clusters para-FH₂⁻, normal-FH₂⁻, FCH₄⁻ and FCD₄⁻. The F + H₂ results improve on previously published photoelectron spectra, resolving a narrow peak that appears in the same position in the para-FH₂⁻ and normal-FH₂⁻ spectra, and suggesting that additional theoretical treatment is necessary to fully describe and assign the experimental results. A small peak in the para-FH₂⁻ results is also identified, matching simulations of a product resonance in the ν′ = 3 vibrational level. SEVI spectra of the ²P_3/2 bands of FCH₄⁻ and FCD₄⁻ show extended structure from transitions to the entrance valley van der Waals region and the reactant side of the F + CH₄ transition state region. Much of this structure is attributed to bending or hindered rotation of the methane moiety and may be a spectroscopic signature of reactive resonances.