The non-statistical dynamics of the 18O + 32O2 isotope exchange reaction at two energies

Abstract

The dynamics of the 18 While the QCT calculations captured the experimental product vibrational energy distribution better than the QS method, the QCT results underpredicted rotationally-excited products, overpredicted forward-bias and predicted a trend in the strength of forward-bias with collision energy opposite to that measured, indicating that it does not completely capture the dynamic behavior measured in the experiment. Thus, these results further underscore the need for improvement in theoretical treatments of dynamics on the O 3 (X 1 A') PES and perhaps of the PES itself in order to better understand and predict non-statistical effects in this reaction and in the 3 formation of ozone (in which the intermediate O 3 * complex is collisionally stabilized by a third body). The scattering data presented here at two different collision energies provide important benchmarks to guide these improvements.

The Role of Ozone Vibrational Resonances in the Isotope Exchange Reaction 16O16O + 18O → 18O16O + 16O: The Time-Dependent Picture

“…The SSB and mSSB PESs were employed by many groups for the theoretical modeling of the isotope exchange dynamics, [6][7][8][9]57,67 using a quantum statistical model, quasiclassical trajectories, and wave propagation method, but it did not produce a satisfactory agreement with observations. [14][15][16][17]57 On the other hand, it was shown that a complete basis set (CBS) limit (either l = 4, l = 5 → ∞, 16,22,25 or l = 5, l = 6 → ∞, 22,26 or l = 3, l = 4 → ∞ 23 ) was necessary to approach the experimental D 0 value. 63,65 At this point, the situation was quite confusing because at the same time the increasing cardinal number of the atomic basis set beyond l = 5 conducted to stretching vibrational ν 1 and ν 3 frequencies, which are significantly larger than the experimental values (Figure 2 in Tyuterev et al 26 ).…”

“…The barrier reef height for the R_PES lies much deeper inside the well (E reef = −320 cm −1 ) in comparison with other PESs, 20,21,25 which exhibited either a true barrier or a reef structure and had been used for the dynamics calculations in the previous works. [6][7][8][9]57,67 For the mSSB or AB surfaces the reef was only about −100 cm −1 below D e (see Table 1). Another important difference is that the R_PES is more attractive on the ozone MEP than the NR_PES just above the TS range (Figure 1), whereas all other published PESs were significantly less attractive than both of them (see Figure 1 of Guillon et al 13 ).…”

First-Principles Computed Rate Constant for the O + O2 Isotopic Exchange Reaction Now Matches Experiment

“…It has been recently demonstrated 38 that a purely statistical approach on the DLLJG PES is not valid for the 18 O + 32 O 2 collisions that seem more likely to be controlled by a pure dynamical behavior. A reliable description of individual quantum vibration−rotation states of the O 3 * intermediate complex in the relatively deep well of the PES during the collision process, from the bottom of the well to the dissociation, is thus necessary for the modeling of this process.…”

Communication: Rigorous quantum dynamics of O + O2 exchange reactions on an ab initio potential energy surface substantiate the negative temperature dependence of rate coefficients

“…29 In our recent work, quantum statistical model (QSM) calculations on the DLLJG PES have already produced a negative temperature dependence for the O + O 2 rate coefficients. 22 However, this QSM-based conclusion is tentative as the O + O 2 exchange reactions are known to have a strong non-statistical character, [30][31][32] accurate description of the kinetics with any form of statistical theory. To provide a conclusive assessment of the DLLJG PES, we report here an extensive quantum dynamics investigation, which computes the rate coefficients and their temperature dependence from state-to-state and initial-state selected integral cross sections.…”