Contribution to the Analysis of the Predissociated Rovibronic Structure

Spectrochimica Acta Part A 60 (2004) 889–898 Contribution to the analysis of the predissociated rovibronic structure of 16 18 −1 the symmetric isotopomers O3 and O3 of ozone near 10,400 cm : 3 ( 2) ← X˜ 1 ( 0) 3 ← X˜ 1 A2 30 A1 00 and B2 A1 G. Wannous a,∗, A.J. Bouvier a, Z. El Helou a, X. Chillier a, S. Churassy a, R. Bacis a, A. Campargue b, G. Weirauch b, R.H. Judge c a Laboratoire de Spectrométrie Ionique et Moléculaire, UMR CNRS No. 5579, Université Claude Bernard Lyon 1, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France b Laboratoire de Spectrométrie Physique, Université Joseph Fourier de Grenoble, BP 87, 38402 Saint Martin d’Hères Cedex, France c Department of Chemistry, University of Wisconsin-Parkside, Kenosha, WI 53141-2000, USA Received 7 March 2003; accepted 9 July 2003 Abstract The absorption spectrum of ozone was recorded at low temperatures (down to −135 ◦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 16 18 spectra of O3 and O3 shows that this spectral region corresponds to a superposition of two different electronic transitions, one with a very 3 broad rotational structure, showing for the first time the asymmetric stretching frequency mode ν3 of the electronic state A2, the other formed 1 3 by a completely diffuse band, probably the 20 band of a new transition due to the triplet electronic state B2. Predissociation effects induce −1 2 3 ← X˜ 1 large broadening of the rotational lines for the transition centered at 10,473 cm identified as the 30 band of the A2 A1 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 ± 3cm−1 and the value of 16 3 −1 3 the O3( A2) antisymmetric stretching frequency mode is equal to 460 ± 2cm . We believe that the diffuse band is due to the B2 state and −1 16 −1 18 18 is located at about 10,363 ± 3cm for O3 and 10,354 ± 3cm for O3. The isotopic rules confirm the different results obtained for O3 16 and O3. © 2003 Elsevier B.V. All rights reserved. 16 18 Keywords: Ozone; O3; O3; Electronic spectroscopy; Wulf transition; Intra cavity laser absorption spectroscopy (ICLAS) 1. Introduction states, we have successfully completed a mixed line-by-line 0 and band contour analysis of the 00 band [10c,14a] of the 3 ˜ 1 Absorption of solar radiation by the ozone molecule plays A2 ← X A1 transition. We have also been able to deter- 3 a major role in the atmosphere through important chemical mine the lifetime of the A2 state [10c,15]. These results transformations in the troposphere, stratosphere and meso- demonstrate the bound and metastable character of this state sphere. As a consequence, extensive theoretical [1–7] and but show that the lifetime is drastically reduced by predis- experimental efforts [8–13] have been undertaken to deter- sociation processes which eliminate the hypothetical role of mine the structure, spectroscopy and excited states of ozone “hidden” ozone in the related excited state for the observed during this last decade. range of high K and high J values. The five lowest-lying excited electronic states of ozone In a review about ozone [16], we suggested that the ab- contribute to the absorption in the near infrared up to vis- sorption spectra recorded by Fourier transform spectrometry, −1 3 ˜ 1 ible region (Wulf and Chappuis bands). For one of these in the region 10,460 cm , involve the B2 ← X A1 transi- −1 1 tion with T0 = 10,458 ± 5cm (1.2966±0.0006 eV). The ∗ Corresponding author. Tel.: +33-4-72-44-85-58; fax: +33-4-72-44-58-71. 1 A manuscript error has been introduced in the paper of [16], page E-mail address: [email protected] (G. Wannous). 20 last line and Table 3 (caption b) maximum peak at 10,456 ± 1cm−1 1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1386-1425(03)00316-0 890 G. Wannous et al. / Spectrochimica Acta Part A 60 (2004) 889–898 Table 1 of all three vibrational modes were calculated theoretically. −1 State Theory Experiment The antisymmetric stretching frequency is 422.2 cm in the a a a diabatic representation with the non-adiabatic coupling and Te (T0) [2] T0 [1a] Te [5] T0 [11] T0 [8] (eV) 427.3 cm−1 from adiabatic PES without the non-adiabatic 3 ± A2 0.90 (0.92) 1.15 0.86 1.18 1.184 0.002 coupling. At the present time, experimental verification of 3 B2 1.19 (1.18) 1.33 1.10 1.30 1.29 ± 0.03 3 this predicted band is lacking. B1 1.18 (1.16) 1.33 1.27 1.45 1.45 ± 0.03 1 =∼ This paper is devoted to an analysis of the complex struc- A2 1.15 (1.14) 1.44 1.44 1.6 −1 1 B1 1.65 (1.64) 1.88 1.82 1.98 ture observed between 10,274 and 10,525 cm that is su- 2 3 ← perimposed on the 20 band of the Wulf transition, A2 T0 (or Te) of the five lowest excited states of the ozone molecule were X˜ 1 calculated using multi-configurational second-order perturbation theory A1 (see Fig. 1a and b). Absorption spectra of both iso- 16 18 (CASPT2) [1a]. The calculation was carried out for the ground and topomers, O3 and O3, have been studied. We have con- seven low-lying singlet and triplet excited states of ozone and the ground cluded that this spectral region is composed of two weak state of ozonide anion in C2v symmetry by the complete active space transitions. The first, located in blue, has a somewhat diffuse self-consistent field (CASSCF) and the multi-reference Meller–Plesset rotational sub-band structure while the other is completely perturbation (MRMP) [2]. Calculated adiabatic energies relative to X˜ 1A 1 diffuse and lacks any resolvable rotational structure. under C2v symmetry as obtained from MRD-CI potential energy surfaces ˜ 1 (X A1 and the first 12 states of the ozone molecule) [5]. From absorption The absorption features of the first transition are spectroscopy [8]. Anion photoelectron spectroscopy [11]. broadened by predissociation and are largely overlapped. a Only the symmetric vibrational modes used for the calculation of This results in a spectrum characterized by broad un- the ZPE corrections. 2 dulations against the background continuum of the 20 3 ˜ 1 A2 ← X A1 transition. Under these conditions, di- rect assignments are not possible. As a consequence, we 3 (3Σ −,v= B2 state shares the same dissociation limit [O2 g have used the band contour method to confirm the na- 3 ˜ 1 3 1 0)+O( P)] as the ground state X A1, the A2 and A2 elec- ture of the transition and to determine approximate val- tronic states. The calculated value of the adiabatic excita- ues of the main spectroscopic constants (rotational and tion energy of the lower excited states has varied during the spin–orbit constants). The geometry of the molecule of last decades [17,18]. But recent ab initio values [1a,2,5] for ozone in the upper vibrational level was determined from 3 the transition to the B2 state have been found to be close the observed constants. The band contour method also to experimental values. Specifically, Allan et al. [12] re- showed that the symmetry of this band is the same as port a value of 1.297 eV (electron-energy loss spectroscopy). 0 1 3 ← X˜ 1 that of the 00 and 20 bands of the A2 A1 transi- Arnold et al. [11] obtained a value of 1.30 eV from the dis- tion. We have justified the assignment of this cold band sociation of the O − anion, and Anderson and co-workers 2 3 as 30 from both theoretical spectroscopic considerations [8,17–19] found 1.29±0.03 eV by absorption spectroscopy. and from a comparison between the spectra of the two These values along with values for other states in this region isotopomers. are summarized in Table 1.In[8], the authors improved their The other transition, in the red side of the region (Fig. 1a results with a spectrometer able to detect ozone absorption and b) and centered at 10,360 cm−1, is structureless and features nine orders of magnitude weaker than the Hartley weak. By comparison of the absorption spectra for the iso- 16 18 bands. They have successfully characterized the energy of topomers O3 and O3, we propose its assignment as 3 3 ˜ 1 the vibrational bands of the three lower triplet states ( A2, B2 ← X A1. This is in agreement with the recent works 3 3 B2, B1) and determined their origin frequencies through a previously mentioned and presented in Table 1. careful investigation from the near infrared to the visible ab- In the following sections, we describe the experiments sorption region using a combination of digital filtering and used to obtain the absorption spectra at low temperatures, isotopic substitution. by Fourier transform spectroscopy (FTS) and intra cavity In a more recent paper [20], these last authors also esti- laser absorption spectroscopy (ICLAS). Section 3 contains mated the value of the asymmetric stretching frequency, ν3, a discussion of the modeling of the different possible tran- 3 −1 of the A2 state to be 367 ± 17 cm from the triplet state sitions including a discussion of the symmetries of the 3 A2 zero point energy.

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