The experimental laboratory frequencies from the millimeter
region were reported in
(1) S. Saito and S. Yamamoto,
1997, J. Chem. Phys. 107, 1732.
The parameters used in the present fit differ slightly from those in (1).
Moreover, the lines omitted from the fit because of overlap or
asymmetric shape due to broad, but unresolved hyperfine
splitting differ from those in (1).
With respect to the Oct. 2003 entry, additional accurate transition
frequencies from the microwave and lower millimeter wave regions
were included, which were published in
(2) H. Ozeki, T. Hirao, S. Saito and S. Yamamoto,
2004, Astrophys. J. 617, 680.
Since the rather complex hyperfine splitting will be
unresolvable at higher frequencies or hard to be resolved at
lower frequencies in warmer inter or circumstellar sources
the main entry does NOT take into account hyperfine
splitting.
NOTE HOWEVER: both the
^{1}H and ^{14}N hyperfine splitting may be
resolvable at lower frequencies and in cooler sources.
Therefore, a
calculation with hyperfine structure
is available with N" up to 10.
Transitions both without and with hyperfine splitting have been
included in the fit. A separate state number was used.
The main entry has been simplified to include only 4 quantum
numbers: N, K_{a}, K_{c},
and J + 1/2; the coding of the quantum numbers has been
corrected with respect to the first entry. The partition
function and the upper state degeneracies of the hyperfine free entry
take into account the hyperfine splittin !
The present predictions with hyperfine splitting also has been
simplified. The state number has been omitted to avoid
confusion. Now the fourth quantum number is an
aggregate spin number.
It can be decoded with part of the
hfs.out file.
The fifth quantum number, F, designates the total spin.
The dipole moment is from an ab initio calculation by
(3) H. S. P. Müller, unpublished.
At low temperatures, it may be necessary to discern between
orthoH_{2}CCN and paraH_{2}CCN.
The ortho states are described by K_{a} even,
the para states by K_{a} odd.
There are three times as many levels for orthoH_{2}CCN
than there are for paraH_{2}CCN.
Thus, for transitions with unresolved ^{1}H hyperfine splitting
the nuclear spinweight ratio is 9 : 3 between
orthoH_{2}CCN and paraH_{2}CCN.
However, for transitions with resolved ^{1}H hyperfine splitting
no nontrivial spinstatistics have to be considered.
The N_{KaKc} = 1_{11};
J + 1/2 = 2 is the lowest para state.
It is 9.8339 cm^{–1} above ground.
