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We investigated the title reaction at collision energy 3.5 kcal mol(-1) in a crossed molecular beam apparatus using undulator radiation as an ionization source. Time-of-flight (TOF) spectra of product C(3)H(3) were measured in laboratory angles from 20° to 100° using two photoionization energies 9.5 and 11.6 eV. These two sets of experimental data exhibit almost the same TOF distributions and laboratory angular distributions. From the best simulation, seven angle-specific kinetic-energy distributions and a nearly isotropic angular distribution are derived for product channel C(3)H(3) + H that has an average kinetic-energy release of 15.5 kcal mol(-1), corresponding to an average internal energy of 33.3 kcal mol(-1) in C(3)H(3). Furthermore, TOF spectra of product C(3)H(3) were measured at laboratory angle 52° with ionizing photon energies from 7 to 12 eV. The appearance of TOF spectra remains almost the same, indicating that a species exclusively contributes to product C(3)H(3); the species is identified as H(2)CCCH (propargyl) based on the ionization energy of 8.6 ± 0.2 eV and the maximal kinetic-energy release of 49 kcal mol(-1). Theoretical calculations indicate that the rapid inversion mechanism and rotation in intermediate H(2)CCCH(2) can result in a forward-backward symmetric angular distribution for product C(3)H(3) + H. The present work avoids the interference of reactions of C((1)D) and C(2) radicals with C(2)H(4) and rules out the probability of production of other isomers like c-C(3)H(3) and H(3)CCC proposed in the previous work at least at the investigated collision energy.

We have measured, by means of ultrafast x-ray absorption and optical spectroscopy, the M-O (M=Fe, Co) and Co-N metal to ligand bond length change as a function of time and the formation and decay of the excited states and intermediate species, after excitation with a 267 nm femtosecond pulse. These experimental data combined with DFT calculations allowed us to determine the mechanism of electron transfer operating in the redox reaction of two metal-ligand complexes, [M(III)(C2O4)3]3- and [Co(III)(NH3)6 ]3+. Based on the data we find that, even though both molecules are excited into their charge transfer band, the redox reaction of [M(III)(C2O4)3]3- proceeds via intermolecular electron transfer while [Co(III)(NH3)6 ]3+ electron transfer mechanism is intramolecular.

The mechanism responsible for the redox reaction of [Co(III)(en)3]Ac3 to Co(II) complex has been determined to be intramolecular electron transfer. It was measured in real time by means of subpicosecond extended X-ray absorption fine structure spectra, EXAFS, and optical experiments and supported by density functional theory calculations. The proposed mechanism is based on histograms of bond length changes of the transient structures measured as a function of time, with subpicosecond time and sub-Angstrom resolution and femtosecond transient spectra and kinetics after excitation with a 267 nm femtosecond pulse. Even though four Fe and Co complexes were excited in the charge transfer band and the photoinduced redox reaction proceeds with similar high redox quantum yield, the dominant electron operating mechanism differs: intramolecular for amine metal complexes and intermolecular for oxalate metal complexes. The ligand orientation degree of freedom and counterion effect are proposed to provide tentative explanation for the electron transfer mechanism.

Using a quadrupole mass filter and vacuum-ultraviolet ionization, we measured the time-of-flight spectra of species at mass-to-charge ratios of m/ z = 45-42 from the reaction of N + SiH 4 in crossed molecular beams. Species with m/ z = 44 and 43 correspond to reaction products HSiNH/SiNH 2 and HSiN/HNSi, respectively; species with m/ z = 45 and 42 are assigned to isotopic variants and daughter ions, respectively, of those two reaction products. We measured the photoionization yields and branching ratios for dissociative ionization of reaction products as a function of photoionization energy. The ionization thresholds of products HSiNH/SiNH 2 and HSiN/HNSi were determined to be 6.7 and 9.2 eV, respectively. Furthermore, we calculated the equilibrium structures, electronic energies, and vibrational wavenumbers of various silicon-nitrogen hydrides H x SiNH y ( x + y = 0-3) using quantum-chemical methods. SiNH 2 (X (2)B 2) and HNSi (X (1)Sigma (+)) are more stable than HSiNH (X (2)A') and HSiN (X (1)Sigma (+)) by 0.82 and 2.81 eV, respectively. SiNH 2 (X (2)B 2), HSiNH (X (2)A'), HNSi (X (1)Sigma (+)), and HSiN (X (1)Sigma (+)) have adiabatic ionization energies of 6.81, 8.19, 10.21, and 10.23 eV, respectively. These experimental and calculated results indicate that SiNH 2 (X (2)B 2) and HNSi (X (1)Sigma (+)) are dominant among isomeric products in the reaction of N + SiH 4. This work presents the first observation of products from the reaction of N + SiH 4 in crossed beams and extensive calculations on pertinent silicon-nitrogen hydrides.

The photodissociation dynamics of the acetone S2 (n, 3s) Rydberg state excited at 195 nm has been studied by using femtosecond pump-probe mass-selected multiphoton ionization spectroscopy. For the first time, the temporal evolutions of the initial state, intermediates, and methyl products were simultaneously measured and analyzed for this reaction to elucidate the complex dynamics. Two mechanisms were considered: (1) the commonly accepted mechanism in which the primary dissociation occurs on the first triplet-state surface, and (2) the recently proposed mechanism in which the primary dissociation takes place on the first singlet-excited-state surface. Our results and analyses supported the validity of the new mechanism. On the other hand, the conventional mechanism was found to be inadequate to describe the observed dynamics. The temporal evolution of methyl products arising from the secondary dissociation of hot acetyl intermediates exhibited a very complex behavior that can be ascribed to the combination of a nonuniform initial vibrational distribution and the competition between dissociation and slow intramolecular vibrational redistribution.