The entry is based on
(1) J. Fisher, G. Paciga, L.-H. Xu, S.B. Zhao, G. Moruzzi, and R. M. Lees, 2007, J. Mol. Spectrosc. 245, 7.
About 550 rotational transition frequencies with microwave accuracy were taken from
(2) R. H. Hughes, W. E. Good, and D. K. Coles, 1951, Phys. Rev. 84, 418;
from
(3) M. C. L. Gerry, R. M. Lees, and G. Winnewisser, 1976, J. Mol. Spectrosc. 61, 231;
from
(4) Y. Hoshino, M. Ohishi, K. Akabane, T. Ukai, S. Tsunekawa, and K.Takagi, 1996, Astrophys. J. Suppl. Ser. 104, 317;
from
(5) A. Predoi-Cross, R. M. Lees, H. Lichau, M. Winnewisser, and J. R. Drummond, 1997, Int. J. Infrared Millimeter Waves, 18, 2047;
and from
(6) M. Ikeda, Y.-B. Duan, S. Tsunekawa, and K. Takagi, 1998, Astrophys. J. Suppl. Ser. 117, 248.
The input data included more than 17000 transitions from (1) based on Ritz analysis of Fourier transform far-infrared spectra in the 15–470 cm^–1 region. The global analysis covered the v_t ≤ 2 torsional states, J_max = 30, and K_max = 15 quantum number ranges. With incorporation of 79 adjustable parameters, the global fit achieved convergence with an overall weighted standard deviation of 1.072, essentially to within the assigned measurement uncertainties of ±50 kHz for almost all of the microwave and millimeter-wave lines and ±6 MHz (0.0002 cm^–1) to ±15 MHz (0.0005 cm^–1) for the Fourier-transform far-infrared measurements.
Based on the global fit results, this database has been compiled containing transition frequencies, quantum numbers, lower state energies and transition strengths (Sμ², converted here to intensities at 300 K as usual), covering v_t ≤ 2, K_max = 15, and J_max = 40 (10 J extrapolation). Along with the calculated transition frequencies, model-dependent uncertainties were also determined from the variance-covariance matrix of the least squares analyses, as usual. Transitions with predicted uncertainties larger than 0.5 MHz should be viewed with some caution, those with uncertainties larger than 5 MHz should be great caution.
State numbers 0, 3, and 6 refer to lines with A symmetry with v_t = 0, 1, and 2; state numbers 1, 4, and 7 refer to lines with E symmetry with K_a ≤ 0 and with v_t = 0, 1, and 2; state numbers 2, 5, and 8 refer to lines with E symmetry with K_a > 0 and with v_t = 0, 1, and 2.
Lower state energies are given referenced to the J = K = 0, A, v_t = 0 level, which is about 127 cm^–1 above the bottom of the torsional potential well.
The partition function consider states with v_t ≤ 3, J ≤ 44, and K ≤ 20. The K levels are sufficient well beyond 300 K, the vibrational and J levels are about sufficient at 300 K.
Experimental microwave and millimeter-wave transition frequencies have not been merged, but are available in a line file.
The experimental dipole moment in several torsional states was reported by
(7) K. V. L. N. Sastry, I. Mukhopadhyay, P. K. Gupta, and J. VanderLinde, 1996, J. Mol. Spectrosc. 176, 38.