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High‐Resolution Infrared Spectroscopy of the v1 + v4 Band of 14NF3:Reductions of the Rovibrational Hamiltonian

“…-Some relations demonstrating the unitary equivalence of the three reductions: The relations between parameters of the D-and Q-reductions were given by Lobodenko et al 11 and Watson et al 12 . Those between the Q-and QD-reductions were proposed by Harder 13 . We assumed that these relations could be applied to ν 1 + ν 4 combination band even they were established for an isolated v t = 1 excited state.…”

“…One of the off-diagonal parameters accounting for ∆(k -λ) ≠ 0 interaction can be refined while the others are fixed, usually to zero value. In the case of an isolated v t = 1 state of a symmetric top, three equivalent D-, Q-and QD-reduction schemes were proposed [11][12][13] : -In the D-reduction, the d and ε parameters of the (0, 3) k-type interaction are constrained to zero, while the r parameter of the (2, −1) λ-type resonance is refined.…”

“…For symmetric tops, it is well known that because of collinearity problems, the molecular parameters of the effective rovibrational Hamiltonian cannot all be determined simultaneously by fitting experimental data. The number of parameters has to be reduced through a unitary transformation called reduction [11][12][13][14][15][16][17] . Many studies were performed [18][19][20][21][22] using this approach.…”