The entry is based on
(1) V. V. Ilyushin, E. A. Alekseev, S. F. Dyubko, I. Kleiner, and J. T. Hougen, 2004, J. Mol. Spectrosc. 227, 115.
The study combines rotational data pertaining to v_t = 0 to 2; several of these data are rovibrational transitions between the torsional states facilitated by torsion-torsion interaction as a consequence of the very low barrier to internal rotation of the methyl group. The v_t = 1 data are entirely from this work. The entire data set was refit by
(2) V. V. Ilyushin, 2017, unpublished.
employing the RAM36 code from
(3) V. V. Ilyushin, Z. Kisiel, L. Pszczółkowski, H. Mäder, and Jon T. Hougen, 2010, J. Mol. Spectrosc. 259, 26.
The calculated frequencies are limited in J (30), frequency (300 GHz), and v_t (2). Nevertheless, the identification of acetamide is possible also in warm sources. Data higher in J, frequency, and v_t have been obtained, but the analysis is complex for several reasons, of which one are perturbations in v_t = 3 by the NH₂ wagging state, which affects lower v_t through torsion-torsion interaction. Transition frequencies with calculated uncertainties of 0.1 MHz and more should be viewed with some caution.
The quantum numbers are J, K_a, K_c, and m. The values 0, –3, and 3 of m correspond to A symmetry states involving v_t = 0, 1, and 2, respectively. The values 1, –2, and 4 of m correspond to E symmetry states involving v_t = 0, 1, and 2, respectively.
Please note: No experimental lines have been merged in the present entry. The list of experimental lines (with reference labels) can be accessed in the catalog archive section.
The partition function takes into account higher torsional states, but no small amplitude vibrations. The NH₂ wagging fundamental is at 259 cm^–1, hence its contributions are very small at 100 K and modest at 150 K. More detailed information is available.
The ground state dipole moment components were determined in
(4) T. Kojima, E. Yano, K. Nakagawa, and S. Tsunekawa, 1987, J. Mol. Spectrosc. 122, 408.