Trajectory study of atomic recombination reactions. VII. Recombination of I and Br atoms

Abstract

. Can. J. Chem. 54, 1535Chem. 54, (1976. Classical 3-D trajectory investigation of bromine and iodine atom recombination reactions in He, Ar, and Xe, performed earlier, are extended, using an improved sampling technique, to include a larger number of trajectories and a wider temperature range (200-1500 K). The three body potential energy surfaces used were assumed to be nearly additive, but otherwise were defined by the existing molecular beam and spectroscopic data and contained essentially no arbitrary parameters. The agreement between computed and experimental rate constants is reasonable, and is best if the third body is heavy and reaction proceeds via a bound complex, such as IXe. Orbiting inert gas -recombining atom intermediate dimers, XM*, where X = I or Br, contribute to the overall recombination reaction via XM* + X + X7 + M reaction, provided M is heavy. If M = He, this reaction path is negligibleat all temperatures studied, again provided that X = I or Br. [Traduit par le journal]

Bound complex and triple collision mechanisms for diatom dissociation and recombination

“…In the reverse process, dissociation of A,, the final step in the collisional excitation of A, to the disReaction [3] is the reverse of [I], and [4] is the reverse of the second step of [2]. By detailed balancing the ratio of rates of [l] and [3] is equal to the ratio of rates of [2] and [4]. It follows that the recombination rate via the triple collision mechanism relative to the recombination rate via the bound complex mechanism is equal to the branching ratio for the possible reactions of M with A,.…”

“…Thus, it is that there are no experimental data concerning the relative rates of [l] and [2] (3,4). These studies indicate that for M = Ar, Xe the bound complex [51 k3 + k4 = J7,t-1(P/2np)1'2 mechanism predominates at low temperatures, the triple collision mechanism at high temperatures x J (87 HlQ( -(8, Hl) exp (-PHI dpdq whereas for M = H~ the triple collision mechanism where YIn, is the phase integral for the vibrational predominates at all temperatures of interest.…”

“…The extended results can be surface along whichf is zero. The function 8 is then The following derivation makes reference to reactions [3] and [4]. Extension to reactions [l] and [2] is effected by a straightforward application of the principle of detailed balancing.…”

“…Extension to reactions [l] and [2] is effected by a straightforward application of the principle of detailed balancing. Semiclassical transition state theory has recently been formulated in one dimension (8) for the reaction scheme represented by [3] and [4]. The theory expresses the rate constant for the overall disappearance of A, by reactions [3] and [4] in terms of a phase space function 8.…”

“…Semiclassical transition state theory has recently been formulated in one dimension (8) for the reaction scheme represented by [3] and [4]. The theory expresses the rate constant for the overall disappearance of A, by reactions [3] and [4] in terms of a phase space function 8. This function is a unit step function, and its discontinuity occurs at the surface in phase space which has been chosen to be the transition state.…”