On the Mechanism of Low-Temperature Termolecular Atomic Recombination

Abstract

Articles you may be interested inLow-temperature noncontact atomic-force microscope with quick sample and cantilever exchange mechanism Rev.A simple theory of gas-phase termolecular atomic recombination kinetics is presented which treats the bound-complex (BC) mechanism in a fashion which parallels the Roberts, Bernstein, and Curtiss resonance theory of the energy-transfer (ET) mechanism. The ET rate constant has a low temperature maximum, but the BC rate constant does not. The contributions of the two mechanisms to the low-temperature recombination of hydrogen atoms, with He, Ar, and H2 as third bodies, are estimated and compared. The presence (absence) of a low-temperature maximum in the observable total rate constant is determined by absence (presence) of bound vibrational levels of the hydrogen-third body van der Waals dimer. Hence, experimental studies of these reactions could yield valuable information about the interatomic potentials.

Gas-phase recombination of chlorine atoms

“…The mixtures obeyed Beer's Law and for 23°, c 24 M~l cm-1 at 365 nm, in good agreement with the data of Gibson and Bayliss.13 After the correlation between the manometric and photometric values for the chlorine pressure was established, the photometric method was used to determine the CI2 pressure in the cell.…”

Self-consistent quantum kinetic theory of diatomic molecule formation

“…Likewise, the recent study of helium TBR 18 calculated the rate constant for single direct pathway (9), so it does not provide a numerical test of the equivalence with indirect pathways. Other studies of TBR 16,17,20 have considered multiple pathways, but these also do not provide a reliable test of the formal proof because they do not include a complete representation of intermediate states along a given pathway. Furthermore, such calculations sum the contributions from each pathway in an incoherent manner which may introduce errors associated with the double-counting of transition probability.…”

“…This formal proof, however, has not been supported in practice. For example, Pack, Snow, and Smith 16 calculated TBR rate coefficients for the ET and Ex mechanisms for hydrogen recombination with H 2 , He, and Ar acting as the third-body. They selected only the longest lived quasibound states and obtained rate constants for the separate mechanisms which were not identical and showed different temperature dependencies.…”

On the Rate Constant for the Association Reaction H + CN + Ar → HCN + Ar

“…There is also some evidence which indicates that direct three-body collisions may become relevant. − In addition, we note that there is not a clear cut distinction between the ET and chaperon mechanisms. Indeed, the latter can be understood within a theoretical framework which parallels the resonance theory of Roberts et al for the ET mechanism. Note that the chaperon and ET mechanisms compete among themselves, their relative importance depending on the nature of the system and reaction conditions, namely temperature and pressure.…”