X-Ray and Inner-Shell Processes
Vol. 1

J. Phys. Colloques 48 (1987) C9-765-C9-768
DOI: 10.1051/jphyscol:19879133

A STUDY OF VIBRONIC COUPLING IN THE [MATH] STATE OF CO⁺₂

P. ROY^{1, 2}, T.A. FERRETT^{1, 3}, V. SCHMIDT^{1, 4}, A.C. PARR^{1, 1}, S.H. SOUTHWORTH^{1, 1}, J.E. HARDIS^{1, 1}, R. BARTLETT^{1, 2}, W. TRELA^{1, 2} and J.L. DEHMER<sup>1, 5

1</sup>  National Bureau of Standards, Radiometric and Radiation Physics Divisions, Gaithersburg, MD 20899, U.S.A.
²  Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A.
³  National Bureau of Standards, Gaithersburg, MD 20899, U.S.A.
⁴  Fakultät für Physik der Universität Freiburg, D-7800 Freiburg, F.R.G.
⁵  Argonne National Laboratory, Argonne, IL 60439, U.S.A.

Résumé
Les effets du couplage vibronique dans l'état [MATH](²∑_g⁺) du CO₂⁺ ont été étudiés pour des photons d'énergies comprises entre 20 et 28,5 eV. Deux analyseurs d'électrons hémisphériques suivis de détecteurs sensibles à la position combinés au rayonnement synchrotron de SURF-II ont permis un analyse vibrationnellement résolve de l'état [MATH](²∑_g⁺). La distribution angulaire caractérisée par le paramètre β de l'état vibrationnel interdit [MATH](1,0,1) se révèle très différent de celle de l'état permis [MATH](0,0,0). Les similarités entre la distribution angulaire (β vs. hν) de l'état interdit [MATH](1,0,1) et celle de l'état [MATH](²∑_u⁺) supportent l'hypothèse de couplage vibronique entre ces deux états comme origine pour la bande interdit.

Abstract
We have studied vibronic coupling in vibrationally resolved photoionization to the [MATH] (²∑_g⁺) state of CO₂⁺ in the photon-energy range hν=20-28.5 eV. The measurements utilize high-resolution hemispherical electron analyzers, equipped with area detectors, and the SURF-II synchrotron radiation source at the National Bureau of Standards. The angular distribution asymmetry-parameters (β) for the allowed [MATH](0,0,0) and forbidden [MATH](1,0,1) (19.747 eV binding energy) peaks are found to be quite different. However, similarities between the [MATH](1,0,1) β curve and that for the [MATH] state suggest that vibronic coupling to the [MATH] (²∑_u⁺) state of CO₂⁺ is the explanation for the intensity of the [MATH] state forbidden band in the first 8 eV above threshold.

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