Several levels of theory for description of isotope effects in ozone: Effect of resonance lifetimes and channel couplings

Abstract

In this paper, two levels of theory are developed to determine the role of scattering resonances in the process of ozone formation. At the lower theory level, we compute resonance lifetimes in the simplest possible way, by neglecting all couplings between the diabatic vibrational channels in the problem. This permits to determine the effect of "shape" resonances, trapped behind the centrifugal barrier and populated by quantum tunneling. At the next level of theory, we include couplings between the vibrational channels, which permits to determine the role of Feshbach resonances and interaction of different reaction pathways on the global PES of ozone. Pure shape resonances are found to contribute little to the overall recombination process since they occur rather infrequently in the spectrum, in the vicinity of the top of the centrifugal barrier only. Moreover, the associated isotope effects are found to disagree with experimental data. By contrast, Feshbach-type resonances are found to make dominant contribution to the process. They occur in a broader range of spectrum, and their density of states is much higher. The properties of Feshbach resonances are studied in detail. They explain the isotopic ζ-effect, giving theoretical prediction in good agreement with experiments for both singly and doubly substituted ozone molecules. Importantly, Feshbach resonances also contribute to the isotopic η-effect, moving theoretical predictions in the right direction. Some differences with experimental data remain, which indicates that there may be another additional source of the η-effect.

An experimental test for the mass independent isotopic fractionation mechanism proposed for ozone

“…Indeed, in most cases, the interaction potentials are not affected by the isotopic substitution and such ratios (as m Rf or m RM in (10)) can be supposed to be mass dependent. This assumption is still theoretically investigated in great details (37,38) .…”

Use of Isotope Effects To Understand the Present and Past of the Atmosphere and Climate and Track the Origin of Life

“…[39][40][41][42][43][44][45][46][47][48][49][50] In aq uantum-mechanicallybased approach, the energies and lifetimes of metastable states of ozone for total angular momentum J = 0w ere calculated using new potential energy surfaces. [39][40][41][42][43][44][45][46][47][48][49][50] In aq uantum-mechanicallybased approach, the energies and lifetimes of metastable states of ozone for total angular momentum J = 0w ere calculated using new potential energy surfaces.…”

“…Thed ifficulty in handling the simultaneous effect in the energy transfer process,zero-point energy effect, h-effect, requires state of art computational ability.T he core of the modeling is the dependence of lifetime upon rotational excitation, asymmetry,a nd connection of their vibrational wave functions to the different exit channels. [46,[48][49][50] Until the recent computation [48][49][50] the resonances were difficult to quantify and are of significance. [47] Them ost precise model to date has folded in symmetry,z ero-point energy,s cattering resonances.…”

“…Ad ifferent approach to modeling has been pursued by Babikov and colleagues. [39][40][41][42][43][44][45][46][47][48][49][50] In aq uantum-mechanicallybased approach, the energies and lifetimes of metastable states of ozone for total angular momentum J = 0w ere calculated using new potential energy surfaces. [40] It is in this specific energy transfer event of the transient ozone species stabilizes during collisions,n ot unlike the approach of Heidenreich and Thiemens [20] but more sophisticated in the modeling and potential energy surface.T he kinetics associated with the excited isotopic species and three exit channels were later included in the calculation as well as the differences in the molecular oxygen and in zero-point energies for the isotopologues.The lifetimes of the different excited states species are also included along with the effects arising from symmetries.The lifetimes were obtained from afull quantum mechanical scattering calculation following ac oupled-channel approach as well as the three-dimensional shapes of the surfaces.…”

“…[47] Them ost precise model to date has folded in symmetry,z ero-point energy,s cattering resonances. [46,[48][49][50] Until the recent computation [48][49][50] the resonances were difficult to quantify and are of significance.…”