Europhys. Lett.
Volume 48, Number 5, December 1999
Page(s) 513 - 518
Section Atomic and molecular physics
Published online 01 September 2002
DOI: 10.1209/epl/i1999-00514-3

Europhys. Lett, 48 (5), pp. 513-518 (1999)

Breakdown of the Born-Oppenheimer approach for a diatomic molecule: LiH in the D state

F. Gemperle 1,2 and F. X. Gadéa 1

1 Laboratoire de Physique Quantique, IRSAMC, Université Paul Sabatier
118, route de Narbonne, 31062 Toulouse Cedex 4, France
2 Department of Mathematics, Faculty of Nuclear Science and Physical Engineering
Czech Technical University - Trojanova 13, 120 00 Praha 2, Czech Republic

(received 23 July 1999; accepted in final form 3 October 1999)

PACS. 31.15Qg - Molecular dynamics and other numerical methods.
PACS. 33.20${\rm -t}$ - Molecular spectra.
PACS. 33.80Gj - Diffuse spectra; predissociation, photodissociation.


Breakdown of the Born-Oppenheimer adiabatic approach is found for the third electronic excited state of LiH of $^1\Sigma$ symmetry. A comparison between adiabatic and vibronic calculations indicates changes in the arrangement of the levels and strong level-shifts, rising up to $\rm 90\;cm^{-1}$. In the present case, the predictions can be easily confirmed by experiment with the help of the rotational constants. The generality of such breakdown of the adiabatic approach for highly excited states of molecular systems (even diatomic) is further discussed by considering the diabatic picture.


Copyright EDP Sciences