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Article

Potential Energy Curves for the ¹Σ⁺ and ^1,3Π States of CO^†

G. J. V

zquez* and J. M. Amero

Instituto de Ciencias F

sicas, Universidad Nacional Aut

noma de M

xico (UNAM), 62210 Cuernavaca, M

xico

H. P. Liebermann

Fachbereich C-Mathematik und Naturwissenschaften, Universit

t Wuppertal, Gauβstraβe 20, D-42119 Wuppertal, Germany

H. Lefebvre-Brion*

Laboratoire de Photophysique Mol

culaire du CNRS, B

timent 213, Universit

Paris-Sud, 91405 Orsay Cedex, France

J. Phys. Chem. A, 2009, 113 (47), pp 13395–13401

DOI: 10.1021/jp902730d

Publication Date (Web): September 17, 2009

†

Part of the “Robert W. Field Festschrift”.

, * Corresponding authors. E-mail: G.J.V., vaztor@fis.unam.mx; H.L.-B., helene.lefebvre-brion@u-psud.fr.

This article is part of the

A: Robert W. Field Festschrift

special issue.

Abstract

Ab initio potential energy curves of CO are calculated to address a number of problems remaining in the interpretation of the experimental VUV absorption spectra. The calculations are of the type SCF MRSD-CI. We employed the aug-cc-pVQZ basis set for both carbon and oxygen, augmented with twelve diffuse functions, of s-, p-, and d-type, located on both atomic centers. We focus on the energy region 85000 cm⁻¹ < E < 110000 cm⁻¹ characterized by strong interactions between Rydberg and valence states. In this work we deal specifically with the ¹Σ⁺, ¹Π, and ³Π states lying in this region. Some of the relevant findings are as follows: The minimum of the C′¹Σ⁺ valence state is found 1920 cm⁻¹ above the value inferred from an extrapolation of experimental data. A new ¹Π valence state, labeled E′, is found to perturb strongly the (X²Σ⁺)3pπ E¹Π Rydberg state. The electrostatic perturbation of the (X²Σ⁺)3pπ c³Π Rydberg state by the k³Π valence state is confirmed. The energy position of the (A²Π)3sσ ³Π state, the triplet companion of the W¹Π Rydberg state, is predicted.