A modified vibron model for polyatomic vibrations:: application to bent XY2 molecules

Some simple modifications of the basic vibron model are explored with the aim at making it more useful for practical spectroscopy, in particular for analysis of the spectra of simple molecules with data extending to higher overtones and combination levels. Inclusion of a realistic potential function for the bending vibration in the model yields improved representation for states involving higher excited bending levels and allows a quick assessment of the molecular potential. Introduction of small vibrationally dependent correction terms into the main parameters of thr model yields a dramatic improvement in the quality of the fits to experimental data as is shown by applications of the modified formulas for the vibrational energy levels to the extensively studied molecules of (H2O)-O-16, (H2S)-S-32, and S-32 O-16(2) This modification leaves the simple form of the basic equations of the model unchanged thus retaining one of the main advantages of the vibron approach to the analysis of spectroscopic data, which makes it possible to complete an adjustment of the parameters of the model very rapidly. Another advantage is the economy of the formulas, which in many cases contain a considerably smaller number of adjustable parameters than conventional power series expressions needed to attain a comparable precision of fit to the observations. (C) 2000 Elsevier Science B.V. All rights reserved.