The High-Resolution Infrared Spectrum of 34S16O2up to 4000 cm-1 J.-M. Flaud, W.J. Lafferty, R.L. Sams, and El Hadji Abib Ngom
Introduction Introduction The spectrum of sulfur dioxide is obviously of interest as an atmospheric pollutant monitoring tool especially after a volcanic eruption. It is also present in the Venus atmosphere and has recently been discovered in the atmosphere of Io. The spectrum of the normal isotopic species, 32S16O2 has been very well studied. However, that of the 34SO2 species which is 4% abundant has only been studied in natural samples. In this work we have recorded the spectra of a number of bands of a sample enriched to 95.3% in 34SO2 and retrieved much improved spectroscopy constants of this isotopic species.
Bands of 34S16O2 The fundamental bands: ν1 (8.7μm),ν2 (19.5μm), ν3 (7.4μm)The combination bands: ν2 + ν3 (5.4μm),ν1 + ν3(4.0μm) 2ν3 (3.7μm)and 2ν1 + ν3 (2.8μm). The hot bands: 2ν2‑ν2, 3ν2‑2ν2, ν1+ ν2‑ ν2, ν2+ν3‑ ν2, ν1+ ν2+ν3‑ ν2 Accurate rotational levels for the: (000), (010), (020), (030), (100), (001), (110), (011), (101), (002), (111), (201) vibrational states.
EXPERIMENTAL DETAILS Sulfur dioxide sample enriched in 34SO2 (95.3 %) Bruker IFS 120 HR (PNNL) evacuated to about 4 Pa (0.030 Torr). Potassium bromide beamsplitter. Detectors: Liquid helium silicon bolometer from 410 cm-1 to 660 cm-1 Mercury cadmium telluride from 1000 cm-1 to 2000 cm-1 Indium antimonide detector from 2200 cm-1 - 3700 cm-1. Pressure measured with three MKS Baratron manometers (1, 10 or 1000 Torr full scale) (stated uncertainty of 0.05 % of full scale). Cells: 19.94 cm cell temperature regulated to 24.36C +/- 0.1 C White type long path cell at room temperature of about 21.5+/- 1.0C
ANALYSIS Initial line assignments performed: either by following line series and using combination differences to verify the J and Ka assignments, or by using predictions based on the corresponding spectra analyzed for the main isotopic species. Then the various ground state combination difference obtained in this work were used together with all existing microwave, sub millimeter and terahertz rotational frequencies to obtain an improved set of ground state rotational constants. Finally these GS constants were used to calculate the upper state energy levels of the assigned bands..
HAMILTONIAN MODELS A-type Watson Hamiltonian written in the Ir representation Except for F = hF Jxy2 CC = i*JyJ2 + ( J-3 - J+3) J± = Jx -/+ iJy
Obs. and calc. spectra of the ν1 band of 34S16O2 showing the distinctive b-type contour of the band.
LINE INTENSITIES Nb of fitted intensities: 359 Weighted Standard Deviation: 0.94D+00 Statistical analysis: 0% <δI/I < 3% 66.6 % of the lines 3% < δI/I < 6% 23.4 % of the lines 6% < δI/I < 12% 10.0 % of the lines Total band intensities (10-17 cm-1 /(molecule cm-2) at 296K
Obs. and calc. transitions of the a-type 111-010 hot band. The transitions of the ν1 + ν3 band are off-scale. The lower-state rotational quantum numbers are given.
Corrections from electron-rotation interaction effects Moments of inertia of 34S16O2 in amu Ǻ2 These moments of inertia have been least squares fit together with those previously obtained for 32S16O2 leading to the equilibrium structural parameters: re(S=O) = 1.4307932(40) Ǻ and <e (O=S=O)= 119.32898(24)o.  J.-M. Flaud and W.J. Lafferty, J. M. S. 16 (1993) 396-402
CONCLUSION Much improved spectroscopic constants of the 34S isotopic species. Accurate line intensities ~3% at best Very precise equilibrium structure