F 1s photoelectron angular distributions detected in coincidence
with the BF2+-F+ ions of BF3 molecules: fragmentation-site
dependence of them
Shota Tsuru1, Takashi Fujikawa1, Tomoya Mizuno2 and Akira Yagishita2
1
Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan
2
Institute of Materials Structure Science, KEK, Tsukuba, Ibaraki 305-0801 Japan
Inner-shell photoelectron angular distributions measured by coincidence experiments are called
molecular frame photoelectron angular distributions (MFPADs). In such experiments the fragment ion pair
detection serves two roles: One is to record the molecular axis, and the other is to select a specific
dissociation channel after the Auger decay. The former is necessarily used in the MFPAD measurements.
However, the latter has not been intensively considered so far.
In this work, we report the F 1s recoil frame photoelectron angular distributions (RFPADs) of BF3
molecules. They were measured at the photoelectron energy of 142 eV. After F 1s photoionization, the core
hole is filled by a valence electron and one or more valence electrons are emitted during Auger decay. Then,
the doubly charged molecular ions of BF32+ produced via normal Auger decay immediately breaks up into
two fragment ions (e.g., BF2+ and F+). Thus, coincidence measurements of the ion pair enable us to
determine the recoil axis of the BF2+-F+ ion pair at the instant of the photoemission, so that RFPADs are
obtainable from the triple coincidence measurements of the ion pair and photoelectron [1].
Here a question arises; whether three equivalent B-F bonds break with equal probability after F 1s
photoionization or not. To answer this question, we employed our simple model [2], based on the multiple
scattering x-ray photoelectron diffraction (XPD) theory [3], to the F 1s RFPADs of BF3. We calculated the
F 1s RFPADs considering the site-dependent bond-breaking probabilities. In the model, the RFPADs are
given by
2
2
2
     z
I kˆ ~

k
Fa
1s
P
Fb

 
k
z
Fa
1s
P
Fc

 
k
z
Fa
1s
Fb(c)
,where P
is a relative bond-breaking probability of B-Fb(c) to that of B-Fa with a 1s hole in the Fa atom,
which is managed as a free parameter in calculations. The RFPADs calculated with a value between 0 and 1
for PFb and PFc reproduced the experimental results well. This implies that the B-F bond with the F 1s hole
breaks preferentially. However the bond breaking of B-F bonds without the F 1s hole also contributes to the
RFPADs.
Fig.1 Scheme of the
experimental geometry
(left) and Dependence
of the F 1s RFPADs
from
BF3,
at
photoelectron
the
energy
of 142 eV, on the
relative bond-breaking
References
[1] T. Mizuno et al., J. Chem. Phys. 136, 074305 (2012).
[2] S. Tsuru et al., Chem. Phys. Lett. 608, 152 (2014).
[3] H. Shinotsuka, H. Arai and T. Fujikawa, Phys. Rev. B 77, 085404 (2008).
probability
bonds (right)
of
B-F