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The reactions of both ground, ³P, and electronically excited, ¹D, oxygen atoms with hydrogen sulfide, H2S, have been investigated by means of the crossed molecular beams method with mass spectrometric detection at different collision energies. Amongst the possible reaction channels those leading to HSO+H for the O(³P) reaction and to HSO/HOS+H and SO+H2 for the O(¹D) reaction have been identified and investigated. The dynamics of the channels leading to HSO/HOS+H are elucidated for the reactions of both states and the trend with increasing the collision energy analyzed. Noteworthily, the formation of SO+H2 products appears to be an open channel for the O(¹D) reaction, at least for the highest collision energy investigated (11.8 kcal/mol). Finally, the recent experimental and theoretical estimates of the enthalpy of formation of the HSO radical have been critically analyzed to evaluate their conformity with the present experimental data. [ABSTRACT FROM AUTHOR]

A combination of flash pyrolysis and molecular beam mass spectrometric techniques is employed to explain the mechanisms related to the thermal decomposition of azidoacetone. The presence of five distinct thermal channels in the process is demonstrated.

Detailed understanding of the mechanism of the combustion relevant multichannel reactions of O(3P) with unsaturated hydrocarbons (UHs) requires the identification of all primary reaction products, the determination of their branching ratios and assessment of intersystem crossing (ISC) between triplet and singlet potential energy surfaces (PESs). This can be best achieved combining crossed-molecular-beam (CMB) experiments with universal, soft ionization, mass-spectrometric detection and time-of-fiight analysis to high-level ab initio electronic structure calculations of triplet/singlet PESs and RRKM/Master Equation computations of branching ratios (BRs) including ISC. This approach has been recently demonstrated to be successful for O(3P) reactions with the simplest UHs (alkynes, alkenes, dienes) containing two or three carbon atoms. Here, we extend the combined CMB/theoretical approach to the next member in the diene series containing four C atoms, namely 1,2-butadiene (methylallene) to explore how product distributions, branching ratios and ISC vary with increasing molecular complexity going from O(3P)+propadiene to O(3P)+1,2-butadiene. In particular, we focus on the most important, dominant molecular channels, those forming propene+CO (with branching ratio ∼0.5) and ethylidene+ketene (with branching ratio ∼0.15), that lead to chain termination, to be contrasted to radical forming channels (branching ratio ∼0.35) which lead to chain propagation in combustion systems. [ABSTRACT FROM AUTHOR]

The photodissociation of ozone has been studied at 193 nm using high resolution photofragment translational spectroscopy. The results show six distinct peaks in the time-of-flight spectra for the O2 product and its momentum-matched O atom counterpart. The translational energy distributions determined from the time-of-flight spectra reveal the production of a range of electronic states of the photofragments. The product electronic states were identified based on the translational energy distributions, with the aid of state-resolved imaging experiments by Houston and co-workers. The results reveal the production of a substantial yield of highly excited triplet states of O2, recently suggested to play an important role in the stratospheric ozone balance. In addition, peaks corresponding to O2(a 1Δg) and O2(b 1Σg+) were observed, the latter confirming a previous report [A. A. Turnipseed et al., J. Chem. Phys. 95, 3244 (1991)]. Evidence was seen for a small contribution from the triple dissociation O3→3O(3P), and insight into the dissociation dynamics for this process was inferred from the translational energy distributions. Branching fractions and angular distributions were measured for all channels. The latter were found in general to yield negative β parameters, in contrast to what is seen at longer wavelengths. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The angular and velocity distribution of CO2 product from the reaction OH+CO at 14.1 kcal/mole collision energy has been obtained in a crossed molecular beam study. The reaction is found to proceed through an osculating HOCO complex living about one rotational period. About 65% of the available energy goes into product translation. [ABSTRACT FROM AUTHOR]

Photodissociation of 1,4 diazine (pyrazine) following 248 nm (S2←S0) and 308 nm (S1←S0) excitation has been studied by photofragment translational spectroscopy. While the latter wavelength was inefficient at generating reactive products, the former wavelength afforded a rich variety of fragments, the most translationally energetic being HCN carrying up to 36 kcal/mol. The implications of this reactive mechanism toward interpretation of vibrational energy transfer experiments from hot ground state pyrazine are considered. The absolute quantum yields [lowercase_phi_synonym](248 nm, 27-A)=0.40±0.10, [lowercase_phi_synonym](248 nm, 27-B)=0.08±.02, [lowercase_phi_synonym](308 nm, 27-B′)=0.003±.001 and the two corresponding translational energy distributions are presented. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]