The dynamics of the reaction H+2+H2→H+3+H, with isotopic variations

Abstract

Analytical potential energy surface for the NH3+H↔NH2+H2 reaction: Application of variational transition-state theory and analysis of the equilibrium constants and kinetic isotope effects using curvilinear and rectilinear coordinates A new potential energy surface for the CH3+H2↔CH4+H reaction: Calibration and calculations of rate constants and kinetic isotope effects by variational transition state theory and semiclassical tunneling calculationsWe performed a merged-beam study of the reactions HD+ +D 2 ---;HDi +D, ..... Dj+H, Di + HD---;HDi + D, ..... Dj+H, in which we measured the absolute reaction cross sections, branching ratios, and product energy distributions over the range of relative kinetic energy from -0.002 to 8 eV. Within the experimental uncertainty all three types of data are identical for the two reactant charge states at initial kinetic energies less than 0.5 eV, leading us to believe that adiabatic charge equilibration between the reactants occurs prior to reaction at these low energies. Diabatic behavior becomes increasingly dominant at higher energies. The reaction mechanism is direct and products are formed with a broad distribution of translational energies. In low energy collisions, on the average, a small fraction of the reaction exothermicity and the reactant excitation energy is converted into translational energy of the products. At higher energies there is a net conversion of translational into internal energy. The reaction energetics are not in agreement with stripping model predictions.

Deviation of the rate of the reaction from Langevin behaviour below 1 K, branching ratios for the and product channels, and product-kinetic-energy distributions

“…This η value significantly differs from the 'statistical' value of 0.5 one would get by drawing either the H-or the D-atom product from the four atoms of the collision complex. This observation indicates that the reaction between H + 2 and H 2 (and deuterated species) follows a fast and direct mechanism, in accord with the results of earlier investigations at higher collision energies [25,[49][50][51][52][53]. The lower yield of the H 2 D + + D product channel compared to that of the HD + 2 + H product channel is also predicted by recent quasi-classical calculations, which determined a branching ratio of about 0.3 at a collision energy of 0.01 meV [54].…”

The H2+ + HD reaction at low collision energies: H3+/H2D+ branching ratio and product-kinetic-energy distributions

“…Deuteration of the H 2 and H 2 + reactants has been successfully used to clarify the reaction mechanism in earlier work at higher collision energies. 34,[47][48][49][50] We have also extended our experimental approach so as to be able to obtain information on the kinetic energy distribution of the product ions, which, through energy-conservation arguments, can be related to the distribution of internal quantum states of the products, as previously demonstrated for these reactions by Pollard et al 34…”

Isotopic exchange processes in cold plasmas of H2/D2 mixtures

“…Te (eV, experiment) Te (eV, model) Ne (cm -3 , experiment and model) 1 7.0±1 7.6 (0.8±0.15)×10 10 T e is given in eV. a) References [44,50]; b) same as D 1 ; c) same as I 1 ; d) same as I 3 ; e) same as I 3 , considering the statistical branching ratio; f) same as I 7 ; g) reference [43]; h) same as T 2 ; i) same as T 1 ; j) reference [43], considering the statistical branching ratio; k) estimated from reference [79], considering the statistical branching ratio; l) branching ratio from [80], rate coefficient estimated from cross section in the same reference; m) from reference [81]; n) from reference [34].…”