Initially, astrophysical measurements are more accurate than those performed in the laboratory. The J = 3 – 2 transition was reported by
(1) E. M. Gregersen and N. J. Evans II, 2001, Astrophys. J., 553, 1042.
The J = 1 – 0 transition was reported by
(2) J. Schmid-Burgk, D. Muders, H. S. P. Müller, and B. Brupbacher-Gatehouse; 2004, Astron. Astrophys., 419 949.
With respect to the Feb. 2004 entry, higher frequency data was included in the fit from
(3) V. Lattanzi, A. Walters, B. J. Drouin, and J. C. Pearson, 2007, Astrophys. J., 662, 771.
While the transition frequencies up to 1.2 THz published in that work agreed with our predictions within their uncertanties of 50 kHz, such an agreement must be viewed as fortuitously since our predictions were based on two transitions only which, interestingly, came from astronomical observations. Moreover, the J" = 12 transition had a predicted uncertainty of 3.4 MHz so that a deviation of 10 MHz would still qualify as in very good agreement.
Predictions beyond 2 THz should be viewed with caution.
In very cold and quiescent sources it may be possible to resolve hyperfine splitting. Therefore, a separate hyperfine calculation up to J" = 2 is provided. Basically, ¹³C spin-rotation coupling is the dominant contribution for J = 2 – 1 and higher while forJ = 1 – 0 ¹H spin-rotation coupling and ¹H–¹³C spin-spin coupling have to be taken into account also. Note: The partion function given below does NOT take into account this splitting ! The partion function has to be multiplied with I(H) × I(¹³C) = 4 when hyperfine splitting is considered !
The dipole moment is assumed to agree with that of the main isotopic species, see e029507.cat.