Ozone electronic structure

Ozone is a singlet, but it has an unusual electronic structure and is thus often difficult to model. An RHF Sfable=Opt calculation finds an RHF— UHF instability, and the... 

The structure of ozone is a well-known pathological case for electronic structure theory. Prior to the QCI and coupled cluster methods, it proved very difficult to model accurately. The following table summarized the results of geometry optimizations of ozone, performed at the MP2, QCISD and QCISD(T) levels using the 6-31G(d) basis set ... 

Anderson, S. M K. Mauersberger, and J. Morton, The Ozone Molecule Isotope Effects and Electronic Structure, in Progress and Problems in Atmospheric Chemistry, Advanced Series in Physical Chemistry (J. R. Barker, Ed.), Vol. 3, pp. 473-499, World Scientific, Singapore, 1995. 

The Ozonide Ion.—The red crystalline substance potassium ozonide, KO3, is obtained by recrystallizing from liquid ammonia the product of reaction of ozone and potassium hydroxide.47 The corresponding ozonides NaO and CsO hasre been shown48 to have magnetic susceptibility corresponding to the presence of the OjT ion with one odd electron. The electronic structure of the ozonide ion is... 

An analysis in terms of VB structures (see exercise 3) shows that this configurational mixing corresponds to approximately 40% diradical character in the wave function for ozone. The RHF wave function, on the other hand, contains only 12% of the diradical VB structure (the result was obtained using Hiickel values for the coefficients of the orbitals (2 11)). It is clear from these considerations that a correct treatment of the electronic structure for the ozone molecule must be based on a multiconfigurational wave function. 

Give a description of the electronic structure of ozone that is consistent with the two 0-0 bond lengths being equal. 

Foresman JB, Frisch JE (1996) Exploring chemistry with electronic structure methods. Gaussian Inc., Pittsburgh, PA, p 118 (ozone) and p 128 (FOOF)... 

Both X-ray crystallography and electronic structure calculations using the cc-pVDZ basis set at the DFT B3LYP level have been employed to study the explosive properties of triacetone triperoxide (TATP) and diacetone diperoxide (DADP).32 The thermal decomposition pathway of TATP has been investigated by a series of calculations that identified transition states, intermediates, and the final products. Calculations predict that the explosion of TATP is not a thermochemically highly favoured event. It rather involves entropy burst, which is the result of formation of one ozone and three acetone molecules from every molecule of TATP in the solid state. 

Theoretical calculations suggest that HNOO has a singlet electronic ground state with considerable diradical character, similar to ozone. HNOO is, therefore, a member of the group of 1,3-dipole molecules whose electronic structure has been described as a resonance of the zwitterionic versus the radical structure. 

Ozone, the triatomic form of oxygen, has the electronic structure... 

Woywod C., Stengle, M., Domcke, W., Flothmann, H. and Schinke, R. (1997) Photodissociation of ozone in the Chappuis band. I. Electronic structure calculations, J. Chem. Phys. 107, 7282-7295. 

The first type of hidden JTE defined above is generated by an excited state with a strong JTE. A straightforward example of such a hidden JTE, the ozone molecule O3, was considered recently [11]. Ab initio calculations of the electronic structure of this molecule were performed by a number of authors. Eigure 2 shows some of the results obtained by means of high-level ab initio calculations for the ground state with geometry optimization [12-14]. 

Several challenges remain for the ultimate practical use of these sensors. The response time of the solid state sensors are short (seconds) for initial sensing, but recovery times range from minutes to hours at room temperature. The stability of the sensor to drift associated with accumulation of fixed charge at interfaces, as well as the high sensitivity to ubiquitous urban pollutants ozone and N02 are problematic. All MPc OTFTs show some response to moisture, and conductivity is also temperature sensitive so that humidity and temperature compensation are essential. On a basic research level, the detailed characterization of charge trapping states, electronic structure, and the interactions with analytes is not yet fully understood on a quantitative theoretical basis. The time response of sensor initiation and recovery is also not understood in a detailed manner. In spite of these limitations, the intrinsic chemical stability of MPc compounds and their compatibility with microsensor array fabrication make these candidate OTFTs for further research and development. 

As a second example we choose the allyl radical, (CH2)(CH)(CH2). Its electronic structure is similar to that of ozone, but with only one electron in the la2 orbital. 

The molecule is planar with C2V symmetry, so the electronic ground state is A2- The dominant electronic configuration is (Ihi) (Ifli)- It is not obvious that the electronic structure should have a multiconfigurational nature, but a calculation using as active the three ir-orbitals with three active electrons shows that the leading configuration has a weight of only 92%, to be compared with 91% in ozone (see below). 

To deal with circumstances such as the bonding in ozone, yet retain Lewis formulas as a useful tool for representing molecular structure, the notion of resonance was developed. According to the resonance concept, when two or more Lewis structures that differ only in the distribution of electrons can be written for a molecule, no single Lewis structure is sufficient to describe its true electron distribution. The true structure is said to be a resonance hybrid of the various Lewis formulas, called contributing structures, that can be written for the molecule. In the case of ozone, the two Lewis formulas are equivalent and contribute equally to the resonance hybrid. We use a double-headed arrow to signify resonance and read it to mean that the Lewis formulas shown contribute to, but do not separately describe, the electronic structure of the molecule. 

As can be seen from Table 2.1, in order to achieve extremely high accuracy for thermochemical data, it is necessary to include contributions from molecular vibrations and from the special theory of relativity. Although computationally expensive, calculations of comparable quality can be carried out routinely for a broad range of molecules containing first-row atoms. For a recent review we refer to reference [11]. Problems occur when the wavefunctions are not dominated by one determinant. A prominent example is the ozone molecule where an error of 10 kj/mol occurs at the CCSD(T) level of theory. As we move down the periodic table relativistic effects become increasingly important and the electronic structure becomes more complicated. It is currently not possible to calculate... 

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