Observation of resonances in the transition state region of the F + NH3 reaction using anion photoelectron spectroscopy

Spectroscopy of radicals, clusters, and transition states using slow electron velocity-map imaging of cryogenically cooled anions

“…120 We recently measured cryo-SEVI spectra of the related system FNH3ˉ to investigate the bimolecular F + NH3 reaction. 50 This reaction has been studied previously by infrared chemiluminescence [121][122][123] and with crossed molecular beams scattering. 124 Potential energy surfaces for this reaction have been reported [125][126] and dynamics on these surfaces were explored using quasi-classical trajectory calculations.…”

“…[100][101] Here, recent results are described in which cryo-SEVI spectra of H2CCˉ and FNH3ˉ are used to probe the transition states for the unimolecular H2CC→HCCH isomerization reaction 13 and the bimolecular reaction F + NH3→HF + NH2. 50 Vinylidene, H2CC, is the simplest carbene and as such is of considerable interest in organic chemistry. 102 As shown schematically in Figure 7a, it lies 1.925 eV above acetylene and can isomerize to HCCH over a small (0.13 eV) barrier.…”

“…[126][127] The relevant energetics and geometries for this system are shown in Figure 9. 50 The reaction is exothermic by 1.3 eV and has a submerged barrier between reactant FNH3 and product FHNH2 complexes. The anion is strongly hydrogen-bonded with a calculated dissociation energy of 0.70 eV and has good geometric overlap with the neutral transition state.…”

“…They lie below the transition state energy and are attributed to resonances associated with the product complex that can undergo vibrational predissociation to NH2 + HF. Quantum dynamics calculations of the resonance wavefunctions 50 show that the peaks correspond to progressions in the NH2HF hindered translational mode at 251 cm -1 and a more complex vibration at 829 cm -1 in which pseudo-rotation of the HF is coupled to NH2 out-of-plane wagging. The out-of-plane motion is activated by the flattening of the NH3 pyrimidal structure in the anion upon photodetachment to the NH2HF product complex.…”

“…46 This perspective focuses on results obtained since then, with particular focus on the cryo-SEVI spectra of NO3¯, 47 the hydrated metal oxide clusters TiO3H2¯ and ZrO2H2¯, [48][49] and the transition state precursor anions H2CC¯ and F¯(NH3). 13,50 In addition, a new experimental direction is discussed in which anions are pre-excited with an infrared (IR) laser prior to photodetachment. [51][52] This IR cryo-SEVI experiment probes the effect of vibrational excitation on the anion photoelectron spectrum and provides a new means to measure the vibrational spectrum of a gas phase negative ion.…”