Ground State Constants A0, DK0 and HK0 of CH3CN

Rotational spectra of isotopic species of methyl cyanide, CH3CN, in their ground vibrational states up to terahertz frequencies

“…Thus, good agreement is not surprising. Trial fits with H K released yielded a value of (155 ± 102) Hz as in Anttila et al (1993). Judging by the D K /A ratio, it is too large by about a factor of 3.…”

Ground state spectrum of methylcyanide

“…The standard polynomial expansion (15a) as well as the Pad e approximant (15b) was used. Both of these numerical models have provided very good fits with nearly identical sets of the rotational and centrifugal distortion parameters (see Table 5, the ''forbidden'' parameters A, D K , and H KKK , insensitive to the allowed rotational transitions, were taken from Anttila et al [40]) and nearly all of the 234 rotational ''hyperfine free'' frequencies were fitted within the experimental accuracy. This fact validates the conformity of the Pad e matrix element with the wellconverging polynomial matrix element; the methylcyanide ground state, at least for small values of the K quantum numbers available in our experimental data set, is nearly this case.…”

“…The simultaneous analysis of the hyperfine and rotational structures (as done in [30], see also [41]) does not seem to be appropriate, since the relative accuracies within the hyperfine multiplet are significantly higher than the absolute accuracies of the rotational frequencies. In addition to this, there are significant pressure shifts of individual lines (often measured at various pressures) that can be in the range [40]. c Fixed.…”

The HITRAN 2004 molecular spectroscopic database

“…Most of the additional groundstate data were published by Cazzoli and Puzzarini [481] and by Müller et al [482] . Information of the K level structure in the ground vibrational state is based on Anttila et al [483] and on the perturbations treated in Ref. [479] .…”