Microwave and FIR spectroscopy of dimethylsulfide in the ground, first and second excited torsional states

Abstract

We present a new global study of the millimeter, submillimeter and far-infrared (FIR) spectra of dimethylsulfide ((CH3)2S). New microwave measurements have been carried out between 49 and 660 GHz using spectrometers in IRA NASU (Ukraine), and PhLAM Lille (France). Pure rotational transitions belonging to the three lowest torsional states (ν11,ν15) = (0,0), (1,0), (0,1) of the molecule as well as to intertorsional transitions (ν11,ν15) = (1,0) ↔ (0,1) observable in the millimeter and submillimeter wave ranges due to intensity borrowing via avoided-crossing interactions were combined with new assignments in the fundamental torsional band (AILES beamline of the synchrotron SOLEIL) and analyzed using a model developed for molecules with two equivalent methyl rotors and C2v symmetry at equilibrium (PAM_C2v_2tops program). The upper limit of the frequency range coverage for the microwave data was extended from 300 GHz to 660 GHz and all symmetry species in the torsional excited states and fundamental torsion band of the molecule were analyzed. The final fit included 87 parameters to give an overall weighted root-mean-square deviation of 0.71 for the dataset with J up to 60 consisting of 22277 microwave line frequencies belonging to the three lowest torsional states (ν11,ν15) = (0,0), (1,0), (0,1) as well as to intertorsional transitions (ν11,ν15) = (1,0) ↔ (0,1) and 5720 FIR line frequencies belonging to the observed fundamental band associated with the methyl-top torsion mode (ν11,ν15) = (0,1) ← (0,0). This investigation presents a twofold expansion in the J quantum number for the ground torsional state (ν11,ν15) = (0,0) and the fundamental torsional band (ν11,ν15) = (0,1) ← (0,0); and significantly extends the analysis for the excited torsional states with one torsional quantum excited (ν11,ν15) = (1,0) and (0,1) for which only 18 transitions with J ≤ 5 were analyzed in previous work.