ИСТИНА

A quantitative study of vibrational resonance phenomena of some triatomic molecules was performed. For their ∼100 lower vibrational energy levels we applied resummation techniques of high-order vibrational Rayleigh-Schrodinger perturbation theory (RSPT) divergent series and compared with the matrix configurational interaction (VCI) method. Resummation with quartic 40-th degree diagonal approximants of a subset of low-lying states restored their correct energies. Considering the perturbation parameter λ as a complex variable, the branch points of solutions were found as roots of the discriminant polynomials. The coincidence of the dominant branch points for pairs of states according to the Katz theorem and the condition |λ| ≤ 1 revealed the resonance couplings. The block-diagonal polyad structure of the studied states was reconstructed and the form of the polyad quantum number was determined.