The torsional fundamental band and high-J rotational spectra of the ground, first and second excited torsional states of acetone

Abstract We present a new global study of the millimeter, submillimeter and far-infrared (FIR) spectra involving the three lowest torsional states of acetone ((CH 3 ) 2 CO). New microwave measurements have been carried out between 34 and 940 GHz using spectrometers in IRA NASU (Ukraine), and PhLAM Lille (France). The FIR spectrum of acetone has been recorded on the AILES beamline of the SOLEIL synchrotron facility. The new data involving torsion–rotation transitions with J up to 90 and K a up to 52 were combined with previously published measurements and analyzed using a model developed recently to study the high resolution spectra of molecules with two equivalent methyl rotors and C 2v symmetry at equilibrium (PAM_C2v_2tops program). The final fit included 117 parameters to give an overall weighted root-mean-square deviation of 0.85 for the dataset consisting of 29584 microwave and 1116 FIR line frequencies belonging, respectively, to the three lowest torsional states (ν 12 ,ν 17 ) = (0,0), (1,0), (0,1) and to the observed fundamental band associated with the methyl-top torsion mode (ν 12 ,ν 17 ) = (0,1) ← (0,0). The high values of rotational quantum numbers involved in this study provide an opportunity to test the performance of the PAM_C2v_2tops program approach for the case of highly excited rotational states.