The entry is a modification of the first entry from Sep. 2000. The main change is a significantly larger dipole moment because of mixing between the two lowest electronic states. The value is much better than the ealier one, but should be taken with some caution. Transition frequencies were reported by
(1) M. Guélin, P. Friberg, and A. Mezaoui, 1982, Astron. Astrophys. 109, 23 (from observations towards TMC 1);
(2) C. A. Gottlieb, E. W. Gottlieb, P. Thaddeus, and H. Kawamura, 1983, Astrophys. J. 275, 916;
and (3) W. Chen, S. E. Novick, M. C. McCarthy, C. A. Gottlieb, and P. Thaddeus, 1995, J. Chem. Phys. 103, 7828.
The present fit is a combined fit of all data mentioned above. Uncertainties in (3) appeared to be too conservative and were reduced. The H centrifugal distortion constant was kept fixed to a value close to that of the lowest excited vibrational state. Transition frequencies with calculated uncertainties exceeding 0.2 MHz should be viewed with caution.
The dipole moment is from a quantum chemical calculation by
(4) T. Oyama, H. Ozaki, Y. Sumiyoshi, M. Araki, S. Takano, N. Kuze, K. Tsukiyama, 2020, Astrophys. J. 890, Art. No. 39.
The partition function of the main species takes into account all states presently available in the CDMS. It is converged fairly well up to about 150 K. Vibrational contributions to the partition function are also available. These should be viewed cautiously because of several estimates concerning vibrational energies.