Spectroscopy of the ground, first and second excited torsional states of acetaldehyde from 0.05 to 1.6 THz

We present a new global study of the millimeter wave, submillimeter wave and THz spectra of the lowest three torsional states of acetaldehyde (CH3CHO). New measurements have been carried out between 0.05 and 1.62 THz using three different spectrometers in IRA NASU (Ukraine), PhLAM Lille (France), and JPL (USA). The new data involving torsion-rotation transitions with] up to 66 and K-a up to 22 were combined with previously published measurements and fitted using the rho-axis-method torsion-rotation Hamiltonian. The final fit used 109 parameters to give an overall weighted root-mean-square deviation of 0.69 for the dataset consisting of 8748, 6959, and 4524 transitions belonging, respectively, to the ground, first, and second excited torsional states and 1481 Delta v(t) not equal 0 FIR transitions belonging to the torsional v(t) = 0 -> 1 and 1 -> 2 bands of the molecule. This investigation presents more than a twofold expansion in the J quantum number and almost fourfold expansion in the frequency range coverage for the acetaldehyde rotational spectrum. (C) 2013 Elsevier Inc. All rights reserved.