No abstract

The rotational and vibrational state distributions of the H2 product from the reactions of translationally excited H atoms with HCl, HBr, and HI at 1.6 eV are probed by coherent anti-Stokes Raman scattering spectroscopy after only one collision of the fast H atom. Despite the high collision energy, only the very exoergic (ΔH=−1.4 eV) hydrogen atom abstraction involving HI leads to appreciable H2 product vibrational excitation. For this reaction the H2 vibrational distribution is strongly inverted and peaks in v′=1, with 25% of the total available energy partitioned to vibration. For the mildy exoergic (ΔH=−0.72 eV) reaction with HBr and the nearly thermoneutral (ΔH=−0.05 eV) reaction with HCl, very little energy appears in H2 vibration, 9% and 2%, respectively, and the vibrational state distributions peak at v′=0. However, in all three reactions a significant fraction, 18% to 21%, of the total energy available appears as H2 rotation. All three reactions show a strong propensity to conserve the translational energy, that is the translational energy of the H2+X products is very nearly the same as that of the H+HX reactants. For the reactions with HCl, HBr, and HI the average translational energy of the products is 1.3, 1.7, and 1.7 eV, respectively, and the width of the translational energy distribution is only about 0.5 eV full width at half maximum. The energy disposal in all three reactions is quite specific, despite the fact that this high collision energy is well above the barrier to reaction in all three systems and a large number of product quantum states are energetically accessible. Only a few of these energetically allowed final states are appreciably populated. Although detailed theoretical calculations will be required to account completely for the state specifity, quite simple models of the reaction dynamics can explain much of the dynamical bias that we observe.

No abstract

We report the first determination of the initial vibrational distribution in the OH product of the reaction between O(1D2) and H2. The measurement was made using a novel time-resolved Fourier transform spectroscopic technique which permits the observation of spectra on a microsecond time scale at a known time after the initiation of a reaction. The result is P(v′=1:2:3:4)=0.29:0.32:0.25:0.13 suggesting that the reaction dynamics involve very large attractive energy release during reagent approach followed by an extremely short-lived interaction leading to products within a few vibrational periods.

No abstract

, 2315 (1986). The vibrational distribution in the OH created by the reaction of O ( ' D 2 ) atoms with NH3 has been recorded directly using low pressure infrared emission spectroscopy. The relative kinetic energy of the reagents is Boltzmann at 300 K. The OH product vibrational levels are populated statistically. indicating that the reaction probably involves a long-lived 0 N H 3 intermediate. There is some evidence that this may not be the case at higher reagent translational energies. 2315 (1986) Faisant appel a la spectroscopie d'emission infrarouge 5 basse pression. on a enregistre directement la distribution vibrationnelle du OH qui est crC6 par la reaction des atomes de O ( ' D , ) avcc le NH3. A 300 K . 1'Cnergie cinktique relative des reactifs est celle de Boltzmann. 11 y a une distribution statistique des niveaux vibrationnels du produit OH et ceci indique que la rkaction implique probablement un interrnkdiare 0 N H 3 posskdant une longue vie. Quelques donnees suggerent que tel ne serait pas le cas 5 des energies de translation des reactifs qui seraient plus elevees.[Traduit par la revue]

The energy disposal and branching ratios in the reactions of O(1D2) with CHCl3 and CHF3 have been measured using an implementation of time-resolved Fourier transform spectroscopy in this laboratory. The infrared emission from the products of the reactions is measured as a function of time after the creation of the O(1D2) atom by UV photolysis of ozone. The reaction with CHCl3 produces OH, HCl, and CO as primary products. The OH vibrational excitation indicates simple abstraction dynamics. The HCl has much lower vibrational excitation, characteristic of a longer-lived insertion-elimination process, which also produces CO in the decomposition of the internally excited Cl2CO product. Only HF is observed in the reaction with CHF3. In this case the vibrational distribution is nonmonotonic, indicating contributions from two microscopic channels, possibly associated with the formation of F2CO in both the ground (X̃ 1A1) and first excited (Ã 1A2) states.

Quasi‐classical trajectory calculations have been performed to investigate the dynamics of the H + HX → H2 + X reactions, where X = Cl, Br, and I. Calculations were performed for two collision energies, 16 and 36 kcal mol−1. The results show that the dynamics of the abstraction reactions at these high collision energies are rather unusual. The product energy and angular distributions can be accounted for by a mechanism that involves an isolated interaction between the two H atoms in the system to form H2 followed by hard‐sphere scattering of this newly formed H2 off the X atom.