Ground state rotational and K = 3 splitting parameters determined from high resolution infrared spectra: H28SiD3, H70GeD3 and H120SnD3

High-resolution (ca. 0.003 cm−1) FTIR spectra in the ν5 range of HSiD3 and monoisotopic H120SnD3 were recorded and analyzed to yield ground state parameters by means of combination differences. The splitting of the ground state K = 3 level into A+ and A− sublevels was detected and could be equivalently accounted for by two different models. Model I involves Δk = ± 3 interactions which affect all K levels. The value of the interaction constant ϵ strongly depends on those of C0 and DK, 0, and J-dependent distortion parameters different to those from model II are obtained. This involves δk = ± 6 interactions which account almost exclusively for the K =3 splitting in the HMD3 molecules, M  Si, Ge and Sn. Also including data for H70GeD3, obtained from a re-analysis of previous ν4 and ν5 spectra for the K = 3 transitions, the following values of the model II splitting parameter h3 were obtained (all in 10−11 cm−1): H28SiD3 3.996(14), H70GeD3 4.058(49), H120SnD3 3.637(33).