Ground and First Excited Torsional States of Acetamide
Vadim V. Ilyushin, E A. Alekseev, S K. Dyubko, I Kleiner, Jon T. Hougen
Recent progress in measuring, assigning and fitting the millimeter wave spectrum of the ground, first and second excited torsional states of the acetamide molecule CH3CONH2 is reported. New measurements of the acetamide spectrum have been carried out between 49 and 149 GHz using the millimeter-wave spectrometer in Kharkov. A set of 879 and 827 new rotational transitions have been assigned to the A and E species, respectively, involving torsion-rotation transitions with J up to 20 and Ka up to 10. The observed spectrum of this low-barrier molecule has been analyzed using the rho-axis-method. After removing the observed hyperfine quadrupole splittings, these new data along with previously published measurements were fitted using 48 parameters to give an overall weighted standard deviation of 0.72 for 759, 587 and 265 lines belonging respectively to the ground, first and second excited torsional states and 95 lines corresponding to vt = 1 transitions observed in the millimeter wave range. Separate rms deviations for the A (25 kHz) and E (27 kHz) species, as well as for the vt = 0 state (26 kHz), vt = 1 (25 kHz), vt = 2 (22 kHz) and vt = 1 transitions (34 kHz) indicate a similar quality of the fit for the two symmetry species and for the three torsional states.