EGAS41 - Swansea University

41 st EGAS CP 34 Gdańsk 2009
Predominant dissociation of the CO ∗ ( D 2 Π ) n(d/s)σ Rydberg
states into the C I ∗ 2s 2 2p 1 n(d/s) + O fragments
A. Ehresmann 1∗ , Ph.V. Demekhin 1 , I. Haar 1 , V.L. Sukhorukov 2
1 Institut für Physik, Universität Kassel, D-34132, Kassel, Germany
2 Rostov State University of TC, 344038, Rostov-on-Don, Russia
∗ Corresponding author: ehresmann@physik.uni-kassel.de
Superexcited states of a molecule serve as doorway states for the effective formation of
neutral fragments above the first ionization potential [1]. It was surprisingly obtained
in [2], that the (c 4 Σ − u ) n(d/s)σ g (v) states of the O 2 dissociate predominantly into the
O I ∗ (2p 3 4 S)n(d/s) states conserving the effective principal quantum number n ∗ of the
Rydberg electron. In the present work we apply photon-induced fluorescence spectroscopy
[3] to investigate fluorescent fragments populated via the neutral dissociation of the vibrationally
excited CO ∗ (D 2 Π) n(d/s)σ(v) states [4].
Cross sections for fluorescence from fragments were measured at the undulator beamline
U125/1 at BESSY II, Berlin, in the spectral range of 115–135 nm as a function of
the exciting-photon energy between 20–25 eV. First experimental indications were found
for a predominant dissociation of the CO ∗ (D 2 Π)n(d/s)σ states into the Rydberg states
of the CI atom conserving the n ∗ of the Rydberg electron.
Relative intensity
[arb. un.]
0.3
0.2
0.1
0.0
CO* (D 2 Π) n(d/s),v
0 1 2 3 4 5 6 7 8 9 5d
0 1 2 3 4 5 6 7 8 9 6s
C I: 2s 2 2p 1 5d/6s −> 2s 2 2p 2 3 P
22.0 22.4 22.8 23.2
Exciting-photon energy [eV]
Figure 1: Cross section for the C I: 2s 2 2p 1 ( 2 P)5d/6s → 2s 2 2p 2 3 P fluorescence.
The latter fact is illustrated in Fig. 1. One can see, that the most prominent resonant
features observed in the cross section for the 2s 2 2p 1 ( 2 P)5d/6s → 2s 2 2p 2 3 P fluorescence
in the CI were assigned to the CO ∗ (D 2 Π)(5d/6s)σ(v) vibrational progressions. Results
of the present measurements are interpreted with the help of the theoretical potential
energy curves of the CO + ion and the molecular orbitals of Rydberg electrons computed
within the single center (SC) approach.
References
[1] Y. Hatano, Phys. Rep. 313, 109 (1999)
[2] H. Liebel, S. Lauer, F. Vollweiler, et al., Phys. Lett. 267, 267 (2000)
[3] H. Schmoranzer, et al., Nucl. Instr. Meth. Phys. Res. A 467-468, 1526 (2001)
[4] A. Ehresmann, etal., J.Phys.B:At.Mol.Opt.Phys. 29,3629(1996); 30,1907(1997)
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