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.
Additional millimeter wave transitions have ben reported
by
(2) C. A. Gottlieb, J. M. Vrtilek, E. W. Gottlieb,
P. Thaddeus, and Å. Hjalmarson,
1985, Astrophys. J. 294, L55.
Further 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.
With respect to the Aug. 2004 entry, additional submillimeter
lines have been reported by
(4) M. Caris, T. F. Giesen, C. Duan, H. S. P. Müller,
S. Schlemmer, and K. M. T. Yamada,
2009, J. Mol. Spectrosc. 253, 99.
These data do not only include pure rotational
transitions, but also transitions between the
higher lying ^{2}Π_{3/2} state
and the ^{2}Σ^{μ} state.
Predictions for the rovibrational transitions
between the lower lying ^{2}Π_{1/2}
state and the ^{2}Σ^{μ}
state, which occur around 1 THz, should be viewed
with some caution; the same applies to all transitions
having predicted uncertainties much larger than 1 MHz.
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 is from an ab initio calculation by
(5) D. E. Woon,
1995, Chem. Phys. Lett. 244, 45.
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).
