Vibrational frequencies of ozone: A multiconfigurational approach

Abstract

The electronic ground state of ozone and, in particular, its equilibrium geometry and harmonic vibration frequencies was studied by a variety of multiconfiguration and single-configuration methods. It is well known that the antisymmetric stretch frequency cannot be correctly obtained by single-reference methods unless at least triple excitations are included. Extensive comparison with other work in the literature shows that basis-set effects must be taken into account since the ω3 frequency is very sensitive to computational details. The multiconfiguration methods are shown to give good results provided that an adequate configuration space is used. In particular, the second-order complete active space perturbation method performs very satisfactorily. Traditional multireference configuration interaction (MRCI) methods, using a few reference functions, do not perform so well. A two-reference CI is able to give reasonable results, but only when the orbitals have been prepared by some properly correlated method. Adding several reference functions gives small improvements, and the result is capriciously dependent on the type of reference functions included. The success of the perturbation method, as well as an extreme type of MRCI, indicates that it is far more important to include a large number of diverse configurations in the reference than to treat the remaining dynamical correlation accurately.

Theoretical Characterization of the Gas‐Phase O3⋅⋅⋅HO Hydrogen‐Bonded Complex

“…[35][36][37][38][39] Thus, for ozone, our results differ from the experimental values by at most 0.024 for the OÀO bond length and by 0.78 for the bond angle, [35] and the agreement with other theoretical studies is similar. [37][38][39] ], where the b 1 and a 2 orbitals constitute the p system of ozone which gives it its special reactivity.…”

The Gas‐Phase Reaction between O3 and HO Radical: A Theoretical Study

“…Regarding the reactants and products (O 3 , HO, O 2 and HO 2 ), our results show that the computed geometrical parameters are in very good agreement with the experimental data and also with other theoretical results. [45][46][47][48][49] Moreover, our calculations predict the reaction in Equation (1) to be exothermic by 42.72 kcal mol With respect to the reaction mechanism, our results depicted in Figure 1 show that the reaction between ozone and hydroxyl radical is a complex process that involves the formation of a pre-reactive O 3 ···HO hydrogen-bonded complex (C1) with subsequent addition of the oxygen atom of the hydroxyl group to one of the terminal oxygen atoms of ozone, thus forming the HO 4 intermediate, which decomposes into HO 2 and O 2 .…”

Rovibronic photoionization dynamics of asymmetric-top molecules

“…Ozone has been the subject of many theoretical and experimental investigations, and it has already been recognized in early ab-initio calculations that configuration interaction must be taken into account for a correct description of its ground state electronic wavefunction (see, e.g., Refs. [96][97][98]). Fig.…”