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 27.2 cm^{–1} above the lowest
rotational state (N = 1, J = 0.5,
F = 0 of the ^{2}Π_{1/2} ladder).
The energy difference is only 9.812 cm^{–1}
for C_{3}D !
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.
With respect to the Aug. 2004 entry, lowN
transitions in the ^{2}Π_{1/2}
spincomponent have been reported by
(2) E. Kim and S. Yamamoto,
2005, J. Mol. Spectrosc. 233, 93.
The D hyperfine structure may be resolvable for transitions
with low values of N. Therefore, a separate
hyperfine calculation is provided up to N = 5.
These predictions should be viewed with some caution
for the higher lying ^{2}Π_{3/2}
spin component as well as for the excited
^{2}Σ^{μ}.
Note: The partition
function given below includes the D hyperfine splitting !
Some caution is advised for transitions with predicted
uncertainties 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 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). Since no rovibrational transitions
have been observed thus far for C_{3}D, predictions
of this type of transitions should be viewed with caution.
