Europhys. Lett.
Volume 76, Number 5, December 2006
Page(s) 808 - 814
Section Atomic and molecular physics
Published online 20 October 2006
Europhys. Lett., 76 (5), pp. 808-814 (2006)
DOI: 10.1209/epl/i2006-10335-x

Counterintuitive effects of the electron correlation in the first-excited $\mth{^1\Sigma^+_g}$ state of the hydrogen molecule

Jian Wang1, 2, J. M. Mercero1, I. Silanes1 and J. M. Ugalde1

1  Kimika Fakultatea, Euskal Herriko Unibertsitatea and Donostia International Physics Center - P.K. 1072, 20080 Donostia, Euskadi, Spain
2  School of Science, Huzhou University - 313000 Huzhou, PRC

received 16 August 2006; accepted in final form 29 September 2006
published online 20 October 2006

The first-excited $^1 \Sigma_g^+$ state of the hydrogen molecule has a potential energy curve with two minima, labeled as E and F, respectively. In the transition from the E minimum to the F minimum, the mean interelectronic distance decreases as the nuclear distance increases, which is in contrast to the behavior of the ground state. Previously the F minimum has been identified as arising from the $(2p\sigma_u)^2$ configuration. Our results suggest that it rather arises from the combination of the $(1s\sigma_g)^2$ and $(1s\sigma_u)^2$ configurations, which leads to the formation of an instant ionic pair, $\chem{H^-+H^+}$, with the unshared electron pair resonating between the two hydrogen nuclei.

31.25.Jf - Electron correlation calculations for atoms and ions: excited states.
31.10.+z - Theory of electronic structure, electronic transitions, and chemical binding.
31.15.Ar - Ab initio calculations.

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