Transition frequencies were taken from
(1) D. R. Herschbach and J. D. Swalen, 1958, J. Chem. Phys. 29, 761;
from
(2) R. A. Creswell and R. H. Schwendeman, 1977, J. Mol. Spectrosc. 64, 295;
and from
(3) B. A. McGuire, P. B. Carroll, R. A. Loomis, I. A. Finneran, P. R. Jewell, A. R. Remijan, and G. A. Blake, 2016, Sciece, in press.
Uncertainties of data in (1) were difficult to evaluate, 250 kHz were assumed here. These data were not merged. Data in (2) appear to be judged conservatively, 20 kHz may be more appropriate. More data extending to higher quantum numbers were reportedly measured, but not published. As explained in (1) and (3), transitions may exhibit small methyl internal rotation splitting. Corresponding frequencies from (3) were averaged. Predictions with uncertainties larger than 0.3 MHz should be viewed with caution.
The dipole moment was determined by
(4) D. R. Herschbach and J. D. Swalen, 1957, J. Chem. Phys. 27, 100.