Reduced Hamiltonian for 0100 and 0001 interacting states of tetrahedral XY 4 molecules: Calculated r 2J 2 and r 2J 3-type parameters for ν2 and ν4 bands of methane

Ambiguity of the effective Hamiltonian for the interacting E and F₂ states of tetrahedral XY ₄ molecules was studied. Unitary transformations to yield a reduced form of the Hamiltonian were suggested, the latter including only empirically determinable parameters. The r ₂J ² and r ²J ³-type spectroscopic parameters for the 0001 and 0100 dyad of CH ₄ molecule were calculated by means of contact transformations. It was shown that sets of spectroscopic parameters derived by several authors for the interacting ν₂ and ν₄ bands of CH ₄ and SiH ₄ may be related via certain unitary transformations.