This is an update of version 1 from Mar. 2000.
The experimental data were summarized by
(1) H. S. P. Müller and F. Lewen,
2017, J. Mol. Spectrosc. 331, 28.
Besides new data betwen 1.37 and 1.5 THz from
that study, transition frequencies were taken mostly
from
(2) H. S. P. Müller, R. Gendriesch, F. Lewen, and G. Winnewisser,
2000, Z. Naturforsch. 55a, 486;
and from
(3) R. Cornet and G. Winnewisser,
1980, J. Mol. Spectrosc. 80, 438.
Additional transition frequencies with ^{1}H hyperfine
splitting were taken from
(4) K. D. Tucker, G. R. Tomasevich, and P. Thaddeus,
1971, Astrophys. J. 169, 429;
and from
(5) K. D. Tucker, G. R. Tomasevich, and P. Thaddeus,
1972, Astrophys. J. 174, 463.
Three more transitions are from
(6) J. C. Chardon, C. Genty, D. Guichon, N. Sungur,
and J. G. Théobald,
1974, Rev. Phys. Appl. 9, 961;
and one more from
(7) D. Dangoisse, E. Willemot, and J. Bellet,
1978, J. Mol. Spectrosc. 71, 414.
The predictions should be accurate enough for all
astronomical observations. Predictions with calculated
uncertainties exceeding 0.2 MHz should be viewed
with caution.
The ^{1}H hyperfine splitting can be resolved for Qbranch
transitions with low values of J and K_{a} = 1.
Transitions with K_{a} = 2 do not show hyperfine
splitting while those with K_{a} = 3 are deemed to be
too high in energy. A separate
hyperfine calculation is provided. The partition function
takes into account the hyperfine splitting.
At low temperatures, it may be necessary to discern between
orthoH_{2}C^{18}O and
paraH_{2}C^{18}O.
The ortho states are described by K_{a} odd,
the para states by K_{a} even.
The nuclear spinweights are 3 and 1 for
orthoH_{2}C^{18}O
and paraH_{2}C^{18}O, respectively.
The J_{KaKc} = 1_{11}
is the lowest ortho state. It is 10.4890 cm^{–1}
above ground.
The dipole moment was assumed to be the same as for the main isotopic
species, see e030501.cat.
