Accurate calculation of vibrational resonances by perturbation theory

We construct rapidly convergent algebraic approximants from the perturbatio n series for anharmonic oscillators and obtain accurate resonance energies for the quartic oscillator with a negative coupling. The approximants take into account analytic properties of the eigenvalues. We compare our results with previous calculations performed by other authors. (C) 1999 Elsevier S cience B.V. All rights reserved.