Knowledge Bank

The further study of ambiguities among $q2J5$ and $q2J6$ terms in effective Hamiltonians for triply degenerate fundamentals of tetrahedral molecules is presented. It is shown that, in agreement with theory, $q2J5$ and $q2J6$ diagonal coupling parameters cannot be considered as constants having definite values for a given $F2$ vibrational state, just like $q2J4$ terms previously studied (VI. G. TYUTEREV, J. P. CHAMPION, G. PIERRE and V. L. PEREVALOV, J. Mol. Spectroso. 105, 113-138 (1984)). The use of reduced Hamiltonians containing fewer (but unambiguous) parameters is suggested and applied to the $\nu 4$ band of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$.