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Photoelectron-photofragment coincidence (PPC) spectroscopy was used to characterize the energetics and dynamics of the OH + CH₄ → H₂O + CH₃ reaction initiated by photodetachment of the OH^–(CH₄) anion complex. PPC measurements at a photon energy of 3.20 eV yielded stable (OH-CH₄ + e^–) and dissociative (OH + CH₄ (ν₁ or ν₃, v = 0, 1) + e^–) channels. The main channel is dissociation to OH + CH₄ + e^– with a low kinetic energy release (KER), peaking at 0.04 eV. Interpretation of the experimental results was supported by quantum chemistry and quasiclassical trajectory calculations. Here, the anion potential energymore » surface was constructed at the correlated coupled cluster singles, doubles, and perturbative triples level with augmented correlation consistent polarized valence triple-zeta basis set, and previously calculated neutral potential energy surfaces were used. Quasiclassical simulation of the dynamics of the OH-CH₄ complex was carried out by selecting the momenta and coordinates from the Wigner distribution for the anion, providing the starting point for 4000 trajectories on the neutral potential energy surface. In agreement with the experimental results, most of the trajectories yield slowly recoiling OH + CH₄ reactants while some are trapped in the entrance channel van der Waals well.« less

The photoexcitation of cold oxyallyl anions was studied below the adiabatic detachment threshold at a photon energy of 1.60 eV. Photodetachment was observed through two product channels, delayed electron emission from a long–lived anionic state and dissociative photodetachment via absorption of a second photon. The former produced stable neutral C₃H₄O, while the latter resulted in the concerted elimination of CO+C₂H₄ products. The neutral oxyallyl singlet state has a barrier–free route to cyclopropanone as well as zwitterionic character with a large charge separation and dipole moment. The role of long–lived dipole–bound resonances built on the singlet state below the detachment thresholdmore » is discussed. Furthermore, these results provide one of the first observations of delayed photoemission in a small cold molecular radical anion, a consequence of the complex electronic structure of the neutral diradical, and provide an example of resonance–mediated control of the photodissociation processes.« less

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Abstract The photoexcitation of cold oxyallyl anions was studied below the adiabatic detachment threshold at a photon energy of 1.60 eV. Photodetachment was observed through two product channels, delayed electron emission from a long‐lived anionic state and dissociative photodetachment via absorption of a second photon. The former produced stable neutral C ₃ H ₄ O, while the latter resulted in the concerted elimination of CO+C ₂ H ₄ products. The neutral oxyallyl singlet state has a barrier‐free route to cyclopropanone as well as zwitterionic character with a large charge separation and dipole moment. The role of long‐lived dipole‐bound resonances built onmore » the singlet state below the detachment threshold is discussed. These results provide one of the first observations of delayed photoemission in a small cold molecular radical anion, a consequence of the complex electronic structure of the neutral diradical, and provide an example of resonance‐mediated control of the photodissociation processes.« less

In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron–photofragment coincidence (PPC) spectroscopy was applied to measure anions at m/z 56 and 57 using a pulsed discharge of glyoxal vapor and N₂O. PPC measurements at a photon energy of 3.20 eV yield photoelectron spectra in coincidence with either neutral photofragments or stable neutral products. The measurements showed that primarily stable neutral products were formed, with photoelectron spectra consistent with the oxyallyl diradical, C₃H₄O, and acetone enolate radical, C₃H₅O. The spectra were also found to have features nearly identical to those reported for OCCO and HOCCO by Sanov andmore » co–workers. Here, the stability of the neutral products, as well as an examination of spectra reported for the oxyallyl anion and acetone enolate show that the previous assignments of OCCO and HOCCO are in error, and are instead attributed here to the oxyallyl diradical, C₃H₄O, and the acetone enolate radical, C₃H₅O.« less

The reaction F + H₂O → HF + OH is a four-atom system that provides an important benchmark for reaction dynamics. Hydrogen atom transfer at the transition state for this reaction is expected to exhibit a strong dependence on reactant vibrational excitation. In the present study, the vibrational effects are examined by photodetachment of vibrationally excited F^-(H₂O) precursor anions using photoelectron-photofragment coincidence (PPC) spectroscopy and compared with full six-dimensional quantum dynamical calculations on ab initio potential energy surfaces. Prior to photodetachment at hν_UV = 4.80 eV, the overtone of the ionic hydrogen bond mode in the precursor F^-(H₂O), 2ν_IHB atmore » 2885 cm^-1, was excited using a tunable IR laser. Experiment and theory show that vibrational energy in the anion can be effectively carried away by the photoelectron upon a Franck–Condon photodetachment, and also show evidence for an increase of branching into the F + H₂O reactant channel. The experimental results suggest a greater role for product rotational excitation than theory. Improved potential energy surfaces and longer wavepacket propagation times would be helpful to further examine the nature of the discrepancy.« less

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Abstract In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron‐photofragment coincidence (PPC) spectroscopy was applied to measure anions at m / z 56 and 57 using a pulsed discharge of glyoxal vapor and N ₂ O. PPC measurements at a photon energy of 3.20 eV yield photoelectron spectra in coincidence with either neutral photofragments or stable neutral products. The measurements showed that primarily stable neutral products were formed, with photoelectron spectra consistent with the oxyallyl diradical, C ₃ H ₄ O, and acetone enolate radical, C ₃ H ₅ O. The spectra were also found to have featuresmore » nearly identical to those reported for OCCO and HOCCO by Sanov and co‐workers. The stability of the neutral products, as well as an examination of spectra reported for the oxyallyl anion and acetone enolate show that the previous assignments of OCCO and HOCCO are in error, and are instead attributed here to the oxyallyl diradical, C ₃ H ₄ O, and the acetone enolate radical, C ₃ H ₅ O.« less