The experimental lines were taken from
(1) Y. Endo, S. Saito, and E. Hirota,
1983, J. Mol. Spectrosc. 97, 204;
from
(2) M. Kajita, Y. Endo, and E. Hirota,
1987, J. Mol. Spectrosc. 124, 66;
and from
(3) L Margulés, E. Herbst, V. Ahrens, F. Lewen,
G. Winnewisser, and H. S. P. Müller,
2002, J. Mol. Spectrosc. 211, 211.
The dipole moment is an estimate from several ab initio
calculations by
(4) H. L. Woodcock, S. S. Wesolowski, Y. Yamaguchi, and H. F. Schaefer, III,
2001, J. Phys. Chem. A 105, 5037.
At low temperatures, it may be necessary to discern between
orthoPH_{2} and paraPH_{2}.
The ortho states are described by K_{a} + K_{c} even,
the para states by K_{a} + K_{c} odd.
There are three times as many levels for orthoPH_{2}
than there are for paraPH_{2}.
Thus, for transitions with unresolved ^{1}H hyperfine splitting
the nuclear spinweight ratio is 3 : 1 between
orthoPH_{2} and paraPH_{2}.
However, for transitions with resolved ^{1}H hyperfine splitting
no nontrivial spinstatistics have to be considered.
The N_{KaKc} = 1_{01};
n, F = 5, 1 (or J, F_{1} = 1.5, 1.0)
is the lowest para state. It is 12.2771 cm^{–1} above ground.
The fourth quantum number is an aggregate spinnumber it can be decoded
with the information provided in the lower part of the
ph2.out file or in the upper part of the
ph2.fit file.
