Investigation of the role of triplet states in the Wulf bands of ozone

Ab initio quantum mechanical study of the O((1)D) formation in the photolysis of ozone between 300 and 330 nm

Spin-allowed production of O((1)D) in the near-UV photolysis of ozone is studied using ab initio potential energy surfaces and quantum mechanics. The O((1)D) quantum yield, reconstructed from the absolute cross sections for eight initial vibrational states in the ground electronic state, is shown to agree with the measurements in a broad range of photolysis wavelengths and temperatures. Relative contributions of one- and two-quantum stretching and bending initial excitations are quantified, with the contribution of the antisymmetric stretch being dominant for lambda < 330 nm. Large scale structures in the low-resolution quantum yield are shown to reflect excitations in the high-frequency short bond stretch in the upper electronic state. Spin-forbidden contribution to the O((1)D) quantum yield at wavelengths lambda > 320 nm is estimated using ab initio energies of the triplet states and their spin-orbit couplings.

New theoretical investigations of the photodissociation of ozone in the Hartley, Huggins, Chappuis, and Wulf bands

We review recent theoretical studies of the photodissociation of ozone in the wavelength region from 200 nm to 1100 nm comprising four major absorption bands: Hartley and Huggins (near ultraviolet), Chappuis (visible), and Wulf (near infrared). The quantum mechanical dynamics calculations use global potential energy surfaces obtained from new high-level electronic structure calculations. Altogether nine electronic states are taken into account in the theoretical descriptions: four 1A', two 1A'', one 3A' and two 3A'' states. Of particular interest is the analysis of diffuse vibrational structures, which are prominent in all absorption bands, and their dynamical origin and assignment. Another focus is the effect of non-adiabatic coupling on lifetimes in the excited states and on the population of the specific electronic product channels.

Spin-orbit mechanism of predissociation in the Wulf band of ozone

Previously calculated resonance widths of the ground vibrational levels in the electronic states 1 (3)A" ((3)A(2)) and 1 (3)A' ((3)B(2)), which belong to the Wulf band system of ozone, are significantly smaller than observed experimentally. We demonstrate that predissociation is drastically enhanced by spin-orbit coupling between 1 (3)A"/X (1)A' and 1 (3)A'/1 (3)A". Multistate quantum mechanical calculations using ab initio spin-orbit coupling matrix elements give linewidths of optically bright components of the right order of magnitude.

Time-dependent density-functional theory calculations of triplet-triplet absorption

We present density-functional theory calculations of triplet-triplet absorption by three different approaches based on time-dependent density-functional theory (DFT): unrestricted DFT linear response, open-shell restricted DFT linear response applied to the triplet state, and quadratic response with triplet excitations applied to the ground state. Comparison is also made with corresponding results obtained by Hartree-Fock and multiconfiguration self-consistent-field response theory. Two main conclusions concerning triplet-triplet transitions are drawn in this study: First, the very good agreement between unrestricted and restricted DFT results indicates that spin contamination of the triplet state is not a serious problem when computing triplet-triplet spectra of common organic molecules. Second, DFT response calculations of triplet-triplet transitions can be affected by triplet instability problems, especially for the combination of DFT quadratic response with functionals containing fractional exact Hartree-Fock exchange.

Contribution to the analysis of the predissociated rovibronic structure of the symmetric isotopomers 16O3 and 18O3 of ozone near 10,400 cm-1): [3A2(3(2)(0)) <-- X1A1(0(0)(0))] and 3B2 <-- X1A1

The absorption spectrum of ozone was recorded at low temperatures (down to -135 degrees C) by high resolution Fourier transform spectrometry and intra cavity laser absorption spectroscopy (ICLAS) near 10,400 cm-1. A preliminary analysis of the rotational structure of the absorption spectra of 16O3 and 18O3 shows that this spectral region corresponds to a superposition of two different electronic transitions, one with a very broad rotational structure, showing for the first time the asymmetric stretching frequency mode nu3 of the electronic state 3A2, the other formed by a completely diffuse band, probably the 2(1)(0) band of a new transition due to the triplet electronic state 3B2. Predissociation effects induce large broadening of the rotational lines for the transition centered at 10,473 cm-1 identified as the 3(2)(0) band of the 3A2 <-- X1A1 electronic transition. The rotational structure cannot be analyzed directly but instead the band contour method was used to confirm the symmetry of the transition and to estimate the spectroscopic constants for the 16O isotopomer. The origin of the band is at 10,473 +/- 3 cm-1 and the value of the 16O3(3A2) antisymmetric stretching frequency mode is equal to 460 +/- 2 cm-1. We believe that the diffuse band is due to the 3B2 state and is located at about 10,363 +/- 3 cm-1 for 16O3 and 10,354 +/- 3 cm-1 for 18O3. The isotopic rules confirm the different results obtained for 18O3 and 16O3.

Spectroscopy and predissociation of the 3A2 electronic state of ozone 16O3 and 18O3 by high resolution Fourier transform spectrometry

A high resolution Fourier transform spectrometry analysis of the rotational structure of the 2(0)1 absorption bands of the 3A2<--X1A1 Wulf transition for the isotopomers 16O3 and 18O3 of the ozone molecule is presented. These bands are very intense compared to the 0(0)0 bands but the predissociation is so strong that the main sub-bands appear as continuous contours. Isolated lines and band contour methods are used together to analyse these two rovibrational bands. The lines corresponding to the F2 component are generally the most intense and isolated. Our data sets for the (0 1 0) level of the 3A2 state are limited to about 102 weakly or unperturbed rotational lines for the 2(0)1 of 16O3 in the range 9620-10,140 cm(-1) and 123 weakly or unperturbed rotational lines for the same band of 18O3. Using for each of them the well-defined ground state parameters, we obtained a standard deviation of about 0.035 cm(-1) in the fit to the lines for 16O3 and 0.027 cm(-1) in the case of 18O3. The rotational constants A, B and C, the three rotational distortion terms deltaK, deltaJK and deltaJ, the spin-rotation constants a0, a and b have been successfully calculated for 16O3 and 18O3 while the spin-spin constants were fixed to their respective values obtained for the origin bands. As is the case for the 0(0)0 band, we have a partial agreement with the isotopic laws for the rotational constants. The geometrical parameters of the (0 1 0) level of 3A2 state for the two isotopomers are close, r = 1.357 A, theta = 100.7 degrees for 18O3 and r = 1.352 A and theta = 100.0 degrees for 16O3. The origin of the 2(0)1 band of 18O3 is red shifted by 7.06(4) cm(-1) with respect to 16O3 2(0)1 band and the two bending mode quanta are, respectively, 528.99(9) and 501.34(7) cm(-1). A preliminary qualitative analysis of the predissociation is given in the particular case of the F2 spin component of 16O3 for 0(0)0 and 2(0)1 bands by the measurement of shifts of positions of some rovibrational levels and the evolution of predissociation broadenings in (Q)Q2 branches. We justify the existence of perturbations in the rovibrational levels of 3A2 state through different interaction types: with the dissociation continuum of the same electronic state or with high vibrational repulsive or weakly bound levels of the ground state.

Contribution to the Analysis of the 3A2 <-- &Xtilde;1A1 "Wulf" Transition of Ozone by High-Resolution Fourier Transform Spectrometry

The analysis of the rotational structure of the high-resolution Fourier transform 0(0)0 absorption spectrum of the 3A2 <-- &Xtilde;1A1 band system of the "Wulf" transition of the isotopomer 16O3 of ozone is reported for the first time. With a near pure case (b) coupling model for the upper triplet state, we have assigned a significant portion of the spectrum, mainly the F1 (J = N + 1) and F2 (J = N) spin components, primarily in the lower frequency region of the band. The lines corresponding to the F3 (J = N - 1) component are weak at lower frequencies and heavily congested in the central and higher frequency regions of the spectrum. Perturbations and predissociation phenomena have reduced the effective lifetime of the metastable 3A2 state and have also limited the number of transitions included in the least-squares fit of the band. Approximately 100 lines have been assigned in the range from 9100-9550 cm-1. Three rotational, three centrifugal distortion, three spin-rotation, and one spin-spin constant were varied. The geometry of the molecule in the 3A2 state, as determined from these constants, is r = 1.345 Å and theta = 98.9 degrees, in good agreement with ab initio results. Copyright 1998 Academic Press.