While the first entry from Dec. 2009 was restricted to ground state data only, the present entry is based on data pertaining to the vibrational states v₈ ≤ 2 and takes into account interactions between these states. Interactions with states v₄ = 1, v₇ = 1, and v₈ = 3 were accounted for through spectroscopic parameters and appropriate interaction parameters. The fit was described in
(1) H. S. P. Müller, L. R. Brown, B. J. Drouin, J. C. Pearson, I. Kleiner, R. L. Sams, K. Sung, M. H. Ordu, and F. Lewen,
2015, J. Mol. Spectrosc. 312, 22.
Vibrational ground state data with ¹⁴N hyperfine splitting were taken from
(2) S. G. Kukolich, D. J. Ruben, J. H. S. Wang, and J. R. Williams, 1973, J. Chem. Phys. 58, 3155;
from
(3) S. G. Kukolich, 1982, J. Chem. Phys. 76, 97;
and from
(4) D. Boucher, J. Burie, J. Demaison, A. Dubrulle, J. Legrand, and B. Segard, 1977, J. Mol. Spectrosc. 64, 290.
Additional, extensive data between 91 ans 790 GHz were taken from
(5) G. Cazzoli and C. Puzzarini, 2006, J. Mol. Spectrosc. 240, 153.
Two K = 14 transitions were taken from
(6) M. Šimecková, Š. Urban, U. Fuchs, F. Lewen, G. Winnewisser, I. Morino, K.M.T. Yamada, 2004, J. Mol. Spectrosc. 226, 123.
Further extensive data up to 1.63 THz were reported in (1) and in
(7) H. S. P. Müller, B. J. Drouin, and J. C. Pearson, 2009, Astron. Astrophys. 506, 1487.
The purely K-dependent terms were determined through ΔK = 3 infrared loops from
(8) R. Anttila, V.-M. Horneman, M. Koivusaari, and R. Paso, 1993, J. Mol. Spectrosc. 157, 198,
and from the interactions treated in (1).
The v₈ = 1 data were mostly taken from (1). Additional millimeter wave data come from
(9) A. Bauer and S. Maes, 1969, J. Phys. (Paris) 30, 169.
The ν₈ data were published by
(10) M. Koivusaari, V.-M. Horneman, and R. Anttila, 1992, J. Mol. Spectrosc. 152, 377.
The v₈ = 2 data as well as the 2ν₈ data were mostly taken from (1). Additional data come from
(11) A. Bauer and S. Maes, 1969, C. R. Acad. Sci. Ser. B 268, 1569,
and from
(12) R. Bocquet, G. Wlodarczak, A. Bauer, and J. Demaison, 1988, J. Mol. Spectrosc. 127, 382.
Parameters of three higher vibrational states were taken from
(13) A.-M. Tolonen, M. Koivusaari, J. Schroderus, S. Alanko, and R. Anttila, 1993, J. Mol. Spectrosc. 160, 554.
Vibrational identifiers in this and related entries are
0 for v = 0 (1 with HFS),
2 for v₈ = 1, l = –1 (4 with HFS),
3 for v₈ = 1, l = +1 (5 with HFS),
6 for v₈ = 2, l = 0 (9 with HFS),
7 for v₈ = 2, l = +2 (10 with HFS),
8 for v₈ = 2, l = –2 (11 with HFS).
Transitions between vibrational states occur in the lower energy entry.
The predictions should be reliable throughout.
¹⁴N hyperfine splitting may be resolvable at low values of J and possibly at the highest K. Therefore, predictions with hyperfine splitting have been provided up to J' = 15 (280 GHz) along with partition function values. The rotational part of the partition function is complete up to 500 K (J up to 140 and K up to 30). Vibrational contributions have been considered in the calculation of the partition function for states up to about 1200 cm^–1. Higher vibrational states contribute to less than 3.0 % at 300 K. Additional information on vibrational states is also available.
At low temperatures, it may be necessary to discern between A-CH₃CN and E-CH₃CN. The A state levels are described by K = 3n, those of E state by K = 3n ± 1. The nuclear spin-weight ratio is 2 : 1 for A-CH₃CN with K > 0 and all other states, respectively. The J_K = 1₁ level is the lowest E state level. It is 5.5803 cm^–1 above ground.
Nov. 2010: separate E and A predictions are available along with separate E and A partition function values. NOTE: Before any analyses are performed treating E and A states separately the effects of optical depth ought to be evaluated carefully ! These data are from the previous entry.
The ground state dipole moment was determined by
(14) J. Gadhi, A. Lahrouni, J. Legrand, and J. Demaison, 1995, J. Chim. Phys. 92, 1984.