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The photodissociation of DNCN following excitation of the C 2A″←X 2A″ electronic transition was studied using fast beam photofragment translational spectroscopy. Analysis of the time-of-flight distributions reveals a photodissociation channel leading to D+NCN competitive with the previously observed CD+N2 product channel. The translational energy distributions describing the D+NCN channel are peaked at low energy, consistent with internal conversion to the ground state followed by statistical decay and the absence of an exit barrier. The results suggest a relatively facile pathway for the reaction CH+N2→H+NCN that proceeds through the HNCN intermediate and support a recently proposed mechanism for prompt NO production in flames. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of the diazomethyl (HCNN) radical have been studied using fast radical beam photofragment translational spectroscopy. A photofragment yield spectrum was obtained for the range of 25 510–40 820 cm-1, and photodissociation was shown to occur for energies above 25 600 cm-1. The only product channel observed was the formation of CH and N2. Fragment translational energy and angular distributions were obtained at several energies in the range covered by the photofragment yield spectrum. The fragment translational energy distributions showed at least two distinct features at energies up to 4.59 eV, and were not well fit by phase space theory at any of the excitation energies studied. A revised C–N bond dissociation energy and heat of formation for HCNN, D0(HC–NN)=1.139±0.019 eV and ΔfH0(HCNN)=5.010±0.023 eV, were determined. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of small I-(H2O)n(n=2–5) clusters excited to their charge-transfer-to-solvent (CTTS) states have been studied using photofragment coincidence imaging. Upon excitation to the CTTS state, two photodissociation channels were observed. The major channel (∼90%) is a two-body process forming neutral I+(H2O)n photofragments, and the minor channel is a three-body process forming I+(H2O)n-1+H2O fragments. Both processes display translational energy [P(ET)] distributions peaking at ET=0 with little available energy partitioned into translation. Clusters excited to the detachment continuum rather than to the CTTS state display the same two channels with similar P(ET) distributions. The observation of similar P(ET) distributions from the two sets of experiments suggests that in the CTTS experiments, I atom loss occurs after autodetachment of the excited [I(H2O)n-]* cluster or, less probably, that the presence of the excess electron has little effect on the departing I atom. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of I3- from 390 to 290 nm (3.18 to 4.28 eV) have been investigated using fast beam photofragment translational spectroscopy in which the products are detected and analyzed with coincidence imaging. At photon energies ≤3.87 eV, two-body dissociation that generates I-+I2(A 3Π1u) and vibrationally excited I2-(X 2Σu+)+I(2P3/2) is observed, while at energies >=3.87 eV, I*(2P1/2)+I2-(X 2Σu+) is the primary two-body dissociation channel. In addition, three-body dissociation yielding I-+2I(2P3/2) photofragments is seen throughout the energy range probed; this is the dominant channel at all but the lowest photon energy. Analysis of the three-body dissociation events indicates that this channel results primarily from a synchronous concerted decay mechanism. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of bare I2− and I2− · Ar at 413 and 390 nm have been investigated using a fast beam instrument coupled with a new photofragment coincidence imaging detector. Results from the application of this technique to the dissociation of I2− and I2− · Ar yielded the dissociation energy of I2− (D0(I2−)=1.012±0.008 eV) and I2−–Ar binding energy (D0(I2−–Ar)=45±8 meV). The experiments show that at these wavelengths, I2− · Ar undergoes three-body dissociation to I− + I* + Ar, with very low momentum in the Ar atom and unequal momentum partitioning between the two I atoms. [Copyright &y& Elsevier]

The photodissociation spectroscopy and dynamics resulting from excitation of the B 2A″←X 2A″ transition of CH2CFO have been examined using fast beam photofragment translational spectroscopy. The photofragment yield spectrum reveals vibrationally resolved structure between 29 870 and 38 800 cm-1, extending ∼6000 cm-1 higher in energy than previously reported in a laser-induced fluorescence excitation spectrum. At all photon energies investigated, only the CH2F+CO and HCCO+HF fragment channels are observed. Both product channels yield photofragment translational energy distributions that are characteristic of a decay mechanism with a barrier to dissociation. Using the barrier impulsive model, it is shown that fragmentation to CH2F+CO products occurs on the ground state potential energy surface with the isomerization barrier between CH2CFO and CH2FCO governing the observed translational energy distributions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]