The cyanobutadiynylide ion has been detected very recently
in the circumstellar shell of IRC +10216. Even though no
laboratory data are available at present, very accurate
ab initio calculations, see below, provide very
reliable spectroscopic parameter. Combined with the
chemistry in that source, the assignment of the
C5N appears to be rather
secure; see also the Molecules in Space section.
Rest frequencies were taken from
(1) J. Cernicharo, M. Guélin, M. Agúndez,
M. C. McCarthy, and P. Thaddeus,
2008, Astrophys. J., accepted.
U33332.3, reported by
(2) K. Kawaguchi, Y. Kasai, S.-I. Ishikawa, and N. Kaifu,
1995, Publ. Astron. Soc. Japan 47, 853;
is, at least in part, due to C5N.
Therefore, this line was also used in the fit.
The 14N hyperfine splitting may be be resolvable for
low values of J. Therefore, a separate
hyperfine calculation is provided up to J" = 4.
The eQq value was taken from C3N;
this is probably a good, but not perfect assumption.
The spin multiplicity gI of 3 for the
14N nucleus is NOT included in the partition function
or in the upper state degeneracy gup
of the general entries. The partition function values have to be
multiplied by 3 if hyperfine splitting is taken into account.
The reported line uncertainties seem to be somewhat conservative;
based on the fit results, they seem to be 2 σ
values.
The predictions are probably reliable up to 200, maybe even
300 GHz.
The dipole moment is from an ab initio calculation
by
(3) P. Botschwina and R. Oswald,
2008, J. Chem. Phys. 129, Art. No. 044305.
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