The RennerTeller effect splits the two Σ components
of the CCH bending mode ν_{4} (≈
600 cm^{–1}) of C_{3}H such that the
lower component ^{2}Σ^{μ}
is only 27.20 cm^{–1} above the lowest rotational
state (N = 1, J = 0.5, F = 0 of the
^{2}Π_{1/2} ladder). This leads to
considerable Coriolis interaction, as shown by
(1) S. Yamamoto, S. Saito, H. Suzuki, S. Deguchi,
N. Kaifu, S.I. Ishikawa, and M. Ohishi,
1990, Astrophys. J. 348, 363.
In the case of CC^{13}CH, this enegy difference is
26.56 cm^{–1}.
In the present fit, all five isotopomers studied by laboratory
spectroscopy were fit together in order to constrain some
higher order constants and the ^{1}H hyperfine
splitting. This is reflected in the code for
the quantum number format.
C_{3}H and C_{3}D experimental lines were
taken from (1).
Additional C_{3}H millimeter transitions
come from
(2) C. A. Gottlieb, J. M. Vrtilek, E. W. Gottlieb,
P. Thaddeus, and Å. Hjalmarson,
1985, Astrophys. J. 294, L55.
Further C_{3}H low frequency transitions were taken
from astronomical observations by
(3) N. Kaifu, M. Ohishi, K. Kawaguchi, S. Saito, S. Yamamoto,
T. Miyaji, K. Miyazawa, S.I. Ishikawa, C. Noumara,
S. Harasawa, M. Okuda, and H. Suzuki,
2004, Publ. Astron. Soc. Japan 56, 69.
Data for the three ^{13}C species
were taken from
(4) M. Kanada, S. Yamamoto, S. Saito, and Y. Osamura,
1996, J. Chem. Phys. 104, 2192.
Predictions for low N transitions should be viewed with
some caution mainly because of the uncertainties in the
^{13}C hyperfine parameters.
Increasing caution is advised for extrapolations beyond the
experimentally accessed ~330 GHz.
The state numbers 0 and 1 refer to the ground
vibrational state and the excited v_{4} = 1,
^{2}Σ^{μ} state, respectively.
The dipole moment was assumed to be the same as for the
main isotopomer, see e037501.cat.
A substantial transition dipole moment between v = 0 and
v_{4} = 1 can be expected – a value of 0.5 D
was assumed in (1). However, because of the large uncertainty
of the band origin, rovibrational transitions were omitted from
the prediction.
