High resolution study of the ν1+2ν2ν2 and 2ν2+ν3ν2 “hot” bands and ro-vibrational re-analysis of the ν1+ν2/ν2+ν3/3ν2 polyad of the 32SO2 molecule

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Abstract

The weak “hot” absorption bands, ν1+2ν2ν2 and 2ν2+ν3ν2, were analysed with high resolution using the Fourier transform interferometer Bruker IFS-120 HR. In order to make possible an analysis of the ν1+2ν2ν2 and 2ν2+ν3ν2 bands, as the first step, we re-analysed considerably the stronger “cold” bands, ν1+ν2 and ν2+ν3, which are located in the same spectral regions. As the result of analysis we obtained about 2650 and 2050 transitions (1069 and 1001 upper state ro-vibrational energy values) with Jmax. = 78, Kamax. = 27 and Jmax. = 68, Kamax. = 24 for the bands ν1+ν2 and ν2+ν3, respectively, that is considerably higher than in the earlier studies of corresponding bands (Jmax. = 33, Kamax. = 7 and Jmax. = 50, Kamax. = 16 for the same bands, ν1+ν2 and ν2+ν3, respectively). A strong local resonance interaction with the 3ν2 band was taken into account, and the set of parameters that reproduce the initial experimental data with an accuracy close to experimental uncertainties, was obtained. The weak ν1+2ν2ν2 and 2ν2+ν3ν2 bands were assigned, and about 870 and 930 transitions (553 and 540 upper state ro-vibrational energy values) with Jmax. = 60 and Kamax. = 20 and Jmax. = 59 and Kamax. = 16 were assigned to the ν1+2ν2ν2 and 2ν2+ν3ν2 bands, respectively. A complete list of assigned transitions is presented, and corresponding spectroscopic parameters are obtained from the fit of assigned transitions (upper energy values).

Research Highlights

► SO2 high-resolution spectrum are recorded in the region 1500–2300 cm−1. ► More than 6500 transitions are assigned to the ν1+ν2, ν2+ν3, and 3ν2 bands. ► Experimental spectrum is filtered from lines of the ν1+ν2, ν2+ν3, and 3ν2 bands. ► 1090 transitions are assigned to the “hot” bands ν1+2ν2ν2 and 2ν2+ν3ν2. ► Spectroscopic parameters of all discussed bands are determined.

Introduction

Sulfur dioxide is an important chemical species in many fields such as chemistry, astrophysics, atmospheric optics, laser techniques, etc. (see, e.g., reviews in Refs. [1], [2]). Therefore, spectroscopic studies of the sulfur dioxide molecule have been made during many years both in the microwave (see, e.g., review in Ref. [3]), and submillimeter wave and infrared regions (see, Refs. [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34]). Recently we fulfilled the analysis of the set of high excited vibrational bands of the SO2 molecule, Refs. [35], [36], [37]. In the present paper we continue our study of the SO2 high-resolution spectra, and the subject of interest now is the weak bands ν1+2ν2ν2 and 2ν2+ν3ν2 (the upper vibrational state, (1 2 0) and (0 2 1)). We also re-analysed the ro-vibrational structure of the considerably stronger bands, ν1+ν2 and ν2+ν3, and more than two times increased the known information about these bands. A strong resonance interaction with the (0 3 0) vibrational state is clearly indicated and discussed.

Section snippets

Experimental details

The spectrum of SO2 in the wavenumber region 1500–2300 cm−1 was measured with the Bruker IFS 120 HR Fourier transform spectrometer in Oulu, Finland. The interferogram was recorded at room temperature with a sample pressure of 0.83 Torr and an absorption path length of 163 m. A Globar source, a KBr beam splitter, and an MCT detector were used. The instrumental resolution due to the path difference and the aperture broadening was 0.0024 cm−1, whereas the Doppler width in the middle of the measured

Description of the spectrum and assignment of transitions

Experimentally recorded spectra in the region of location of the strong bands, ν1+ν2 and ν2+ν3, are shown in the upper parts of Fig. 1, Fig. 2 (Fig. 1, Fig. 2, respectively). In both cases, all three branches, P, Q, and R, are clearly pronounced. In the first case (Fig. 1), the upper vibrational state is of A1 symmetry and therefore the observed transitions are of b-type. In this case, one can see a strong Q-branch typical for such type of bands. In the second case (Fig. 2), the upper

Hamiltonian model and determination of spectroscopic parameters of the ν1+ν2/ν2+ν3/3ν2 polyad

The Hamiltonian model employed was taken from Refs. [40], [41]. However, for the convenience of the reader, we briefly reproduce it here. Because strong local interaction was found between the vibrational states (1 1 0) and (0 3 0), the corresponding Fermi-type interaction operator was taken into account in the Hamiltonian model used for analysis of energy values from Table 1. In this case, in spite of the very small absolute value of the corresponding interaction parameter, an introduction of such

Analysis of the “hot” bands, ν1+2ν2ν2 and 2ν2+ν3ν2

As the next step of our analysis, we constructed simulated spectra of the studied bands, ν1+ν2 and ν2+ν3 (see, Fig. 1, Fig. 2, Fig. 3, Fig. 4). In this case, in construction of the simulated spectra only relative line intensities were calculated. As the analysis showed, the correct spectrum for the ν2+ν3 band can be simulated with only one main effective dipole moment parameter. At the same time, for simulation of the spectrum in the region of the ν1+ν2 band, it is necessary to use, at least,

Conclusion

We re-analysed the high resolution ro-vibrational structures of the ν1+ν2 and ν2+ν3 vibrational bands and, as a result, assigned about 2.5 times more transitions than was made before. Some transitions belonging to the 3ν2 band and caused by the strong Fermi interaction between the (1 1 0) and (0 3 0) states were also assigned. Then the experimental spectrum was filtered by taking the lines belonging to the “cold” bands, ν1+ν2, ν2+ν3, and 3ν2, and transitions belonging to the weak “hot” bands, ν1+2ν2

Acknowledgements

Part of the work benefited from the joint PICS grant of CNRS (France) and RFBR (Russia), 4221N0000211752a, from the Russian Science and Innovations Federal Agency under contract No. 02.740.11.0238, and from Russian Federal Agency of Education under contract No. P2596.

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    As a consequence, numerous spectroscopic studies of the sulfur dioxide molecule have been made during many years both in the microwave, submillimeter wave and infrared regions (see, e.g., Refs. [8,5] where extensive references to earlier studies of sulfur dioxide spectra can be found). The generation and spectroscopy of the 32S18O2 and 34S16O2 sample are described in Refs. [15,26] in Refs. [16–25], respectively, and will not be further discussed here. The 32S16O18O sample was generated in the Infrared Lab in Braunschweig in two steps.

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