NOTE: The v₁₂ = 1 state at 769 K is the seventh excited state of ethyl cyanide. Even tough it is relatively isolated, there may be transitions which show methyl internal rotation splitting, especially b-type transitions. The current entry only deals with the A symmetry species and may thus account for half of the intensity if the modeling is focused on the weak, here split, transitions. The methyl internal rotation splitting appears to be rarer than for v₂₀ = 1. Some transitions appear to be perturbed, especially at higher J or K_a, and these perturbations appear to be more prevalent than for v₂₀ = 1.
The observed transitions were summarized by
(1) A. M. Daly, C. Bermúdez, A. López, B. Tercero, J. C. Pearson, N. Marcelino, J. L. Alonso, and J. Cernicharo, 2013, Astrophys. J. 768, Art. No. 81. Besides new spectral recordings, data were extracted from spectra published by
(2) J. C. Pearson, K. V. L. N. Sastry, E. Herbst, and F. C. De Lucia, 1994, Astrophys. J. Suppl. Ser. 93, 589;
from
(3) Y. Fukuyama, H. Odashima, K. Takagi, S. Tsunekawa, 1996, Astrophys. J. Suppl. Ser. 104, 329;
from
(4) C. S. Brauer, J. C. Pearson, B. J. Drouin, and S. Yu, 2009, Astrophys. J. Suppl. Ser. 184, 133;
and from
(5) S. M. Fortman, I. R. Medvedev, C. F. Neese, and F. C. De Lucia, 2010, Astrophys. J. 725, 1682.
NOTE: The spectroscopic parameters are different from those in (1). Several more higher J or K_a transitions were weighted out than in (1) for consistency reason. Perturbations, blending, or possibly misassignments may cause deviations from calculated positions several times (usually four) larger than assigned. Some high J, low K_a transitions weighted out in (1) were weighted in here. Please check the output of the fit file for transitions having the same K_a and a similar J in case of issues with one of not too many problematic lines. Extrapolation may be possible to slightly higher J for lower values of K_a, but should always be viewed with caution. Only fully weighted transitions have been merged.
NOTE: The partition function takes into account energy levels up to J = 150 and K_a = 70. This is sufficient up to 300 K. At higher temperatures classical extrapolations are recommended. Already somewhat below 200 K it may be necessary to correct the partition function values for contributions from low-lying vibrational modes. Vibrational correction factors have been derived in the harmonic approximation. Errors caused by this approximation are probably small.
The ground state dipole moment was taken from
(9) A. Krasnicki and Z. Kisiel, 2011, J. Mol. Spectrosc. 270, 83.