An isotopic invariant fit CO⁺ of data was performed as described in
(1) S. Spezzano, S. Brünken, H. S. P. Müller, G. Klapper, F. Lewen, K. M. Menten, and S. Schlemmer, 2013, J. Phys. Chem. A 117, 9814.
Transition frequencies for the main isotopolog were mostly taken from (1) and from
(2) M. Bogey, C. Demuynck, and J. L. Destombes, 1983, J. Chem. Phys. 79, 4704.
Additional data were taken from
(4) K. V. L. N. Sastry, P. Helmlnger, E. Herbst, and F. C. De Lucia, 1981, Astrophys. J., 250, L91;
and from
(5) F. C. van den Heuvel and A. Dymanus, 1982, Chem. Phys. Lett. 92, 219.
Data for ¹³CO⁺ and C¹⁸O⁺ come from (1) and (2) while those for ¹³C¹⁸O⁺ are entirely from (2).
Also used in the fit were infrared transitions published by
(6) P. B. Davies and W. J. Rothwell, 1985, J. Chem. Phys. 83, 5450.
Two pairs of transitions (N = 8 – 9 and 5 – 4) with residuals much larger than the uncertainties were omitted. In addition, Y₂₀ and Y₃₀ were taken from
(7) W. Szajna, R. Kepa, and M. Zachwieja, 2004, Eur. Phys. J. D 30, 49.
Predictions beyond 1.5 THz should be viewed with some caution.
The dipole moment was assumed to agree with that in the ground vibrational state. Its value was published by
(8) J. K. Thompson, S. Rainville, and D. E. Pritchard, 2004, Nature 430, 58.