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

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 v' = 3 vibrational level. SEVI spectra of the 2P3/2 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.