Chemistry Reference
In-Depth Information
(D). One of the most puzzling spectral characteristics in the energy region in
question is the lower-energy part
539 eV observed in the experiment: a very long
energy tail and a sharp first peak followed by some smaller peaks [23, 26, 33,
34, 91, 102, 104-116]. The accepted interpretation of this feature is that the main
intensity arises from the dissociative
σ
∗
(D) resonance, which is lower than
σ
∗
(Q) due to exchange interaction of the
σ
∗
electron [23, 83]. On the other hand, the
fine features
∼
∼
539 eV were interpreted as a weak vibrational progression in the
bound 3s(Q) state embedded in the
σ
∗
(D) manifold [23] and a Fano profile due to
weak interaction between the bound and continuum-like state [26]. The interaction
between the 3s(Q) and
σ
∗
(D) states could be small, because they have different
ion cores Q and D and 3s and 2p
σ
∗
have different orbital characters [26]. However,
σ
∗
(D) can be mixed with
σ
∗
(Q) [83, 102, 108], and the small
σ
∗
(Q) component
would contribute to interaction with 3s(Q). On the other hand, the strong Rydberg-
valence mixing between 2p
σ
∗
(Q) and 3p
σ
(Q) is found in the higher energy part
∼
542 eV [26, 34, 91, 105], as shown in Fig. 15.
The theoretical spectra produced by the coupled wave-packet propagation in
the diabatic states [108] are shown in Fig. 16 in comparison with the experimental
spectra. In Fig. 16, the partial contributions of the Q and D channels are shown
by ignoring the weak coupling between them. The overall spectral shapes of both
partial cross-sections have roughly Gaussian shapes owing to absorption to the
C
B
O
2
σ
*, Ry
expt.
I
0
Q
theo.
I
0
Q
D
D
536
537
538
539
540
541
542
543
544
Photon energy (eV)
Figure 16.
Comparison between theoretical and experimental
I
0
(
=
0
,
) spectra of O
→
σ
∗
and Rydberg region of O
2
[108]. The theoretical spectrum is decomposed into the quartet
(Q) and doublet (D) ionization channels.
1s
