Notes. Values in parentheses represent 1σ uncertainties, expressed in units of the last quoted digit. ^(a)Parameters converted from Watson A-reduction Hamiltonian to S-reduction (see text). ^(b)Values reported in Ohshima & Endo (1996) are actually B_eff = (B + C)/2 and D_eff = D_J + (B − C)²/{32[A − (B + C)/2]}. ^(c)Alessandrini et al. (2018).^(d) Fixed to the value derived in Nakanaga & Amano (1987).^(e) Fixed to the ab initio value. ^(f)Dimensionless rms, defined as ${\sigma }_w=\sqrt{\frac{{\displaystyle {\sum }_i{({\delta }_i/er{r}_i)}^2}}{N}}$, where the δs are the residuals weighted by the experimental uncertainty (err) and N the total number of transitions analysed.