Description:
<jats:title>Abstract</jats:title><jats:p>The interaction energies in the ground (<jats:italic>X</jats:italic><jats:sup>1</jats:sup>Σ<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/tex2gif-stack-1.gif" xlink:title="urn:x-wiley:00207608:media:QUA560050106:tex2gif-stack-1" />) and the first excited (<jats:italic>b</jats:italic><jats:sup>3</jats:sup>Σ<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/tex2gif-stack-2.gif" xlink:title="urn:x-wiley:00207608:media:QUA560050106:tex2gif-stack-2" />)states of the hydrogen molecule were calculated using the modified Jansen and Byers Brown perturbation method. Calculations were performed for nine values of the internuclear distance <jats:italic>R</jats:italic> in the range 5 a.u. ≦ <jats:italic>R</jats:italic> ≦ 9 a.u. The present results were compared with the interaction energies calculated by four other perturbation methods as the expectation values of the <jats:italic>H</jats:italic> – <jats:italic>E</jats:italic><jats:sup>0</jats:sup> operator with the function accurate up to the first order. The results show that the method can give satisfactory values of the interaction energies.</jats:p>