A study of the bending motion in tetratomic molecules by the algebraic operator expansion method

Danielle Larese; Mark A Caprio; Francisco Pérez-Bernal; Francesco Iachello

doi:10.1063/1.4856115

A study of the bending motion in tetratomic molecules by the algebraic operator expansion method

J Chem Phys. 2014 Jan 7;140(1):014304. doi: 10.1063/1.4856115.

Authors

Danielle Larese¹, Mark A Caprio², Francisco Pérez-Bernal³, Francesco Iachello⁴

Affiliations

¹ Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, USA.
² Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556-5670, USA.
³ Depto. de Física Aplicada, Unidad Asociada CSIC-IEM, Facultad de CC. Experimentales, Universidad de Huelva, Huelva 21071, Spain.
⁴ Center for Theoretical Physics, Yale University, New Haven, Connecticut 06520-8120, USA.

PMID: 24410226
DOI: 10.1063/1.4856115

Abstract

We study the bending motion in the tetratomic molecules C2H2 (X̃ (1)Σg (+)), C2H2 (Ã (1)Au) trans-S1, C2H2 (Ã (1)A2) cis-S1, and X̃ (1)A1 H2CO. We show that the algebraic operator expansion method with only linear terms comprised of the basic operators is able to describe the main features of the level energies in these molecules in terms of two (linear) or three (trans-bent, cis-bent, and branched) parameters. By including quadratic terms, the rms deviation in comparison with experiment goes down to typically ∼10 cm(-1) over the entire range of energy 0-6000 cm(-1). We determine the parameters by fitting the available data, and from these parameters we construct the algebraic potential functions. Our results are of particular interest in high-energy regions where spectra are very congested and conventional methods, force-field expansions or Dunham-expansions plus perturbations, are difficult to apply.