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Cite this: Phys. Chem. Chem. Phys.,2015, 17, 18337

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Fluorination-dependent molecular orbital
occupancy in ring-shaped perfluorocarbons†
Tim Brandenburg,ab Tristan Petit,a Antje Neubauer,a Kaan Atak,abMasanari Nagasaka,c Ronny Golnak,ab Nobuhiro Kosugi*c and Emad F. Aziz*abc
Perfluorocarbons are a family of molecules consisting mainly of carbon and fluorine atoms. They haveinteresting chemical properties and have diverse applications in biomedicine, physical chemistry and polymer
science. In this work, carbon K-edge absorption and emission spectra of liquid decalin are presented andReceived 3rd March 2015,
Accepted 17th June 2015

compared to perfluorodecalin. A comprehensive picture of the electronic structure of decalin is provided

DOI: 10.1039/c5cp01254f

time-dependent density functional theory for the hydrocarbon, the perfluorocarbon and the stepwise

based on soft X-ray absorption and emission spectroscopies. Experimental data are compared to theoretical
fluorinated derivatives. We observed a molecular orbital change from unoccupied to occupied orbitals

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for perfluorodecalin, which was induced through the fluorination process.

1 Introduction
The family of perfluorocarbons has a wide range of applications inbiomedicine and physical chemistry due to their extraordinary
properties.1,2 Many liquid perfluorocarbons are known to show highdensity, high viscosity as well as an especially high gas solubility, andare often chemically and biological inert.3,4 Their ability to dissolve
gases and their biological inertness are exploited in applications,such as tissue oxygenation5–7 or post-operative treatment.8,9The perfluoro eﬀect, inherent to all perfluorocarbons, describes
the energetic shifts of the spectral features upon complete
fluorination of hydrocarbons.10–13 This also led to a generalrule for the dimensions of the energetic shifts depending on
s- or p-character of the molecular orbitals (MO).11,12 Hence, thiseffect can be used for experimental orbital classification. In thiscontext, a few experimental studies have already been performed in
the 1970s.11,12 Many of them were based on photoelectron and X-ray
absorption (XA) spectroscopy.10–14 Since then, more complex
theoretical models15 and the introduction of new experimental
techniques16–18 give opportunities to investigate perfluorocarbons.
Perfluorodecalin (PFD) is often studied as a general model
system for perfluorocarbons. It exhibits the special chemical
properties of perfluorocarbons3,11,19,20 and is frequently used inapplications.5,7–9 In a previous study of the electronic structureaInstitute of Methods for Material Development,
Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15,12489 Berlin, Germany. E-mail: emad.aziz@helmholtz-berlin.deb
Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin,
GermanycInstitute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan.
E-mail: kosugi@ims.ac.jp† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5cp01254f

This journal is © the Owner Societies 2015of PFD weak intermolecular interactions and high inertness
were traced back to a large energetic gap between the highest
occupied MO (HOMO) and the lowest unoccupied MO (LUMO)
and to the geometrical structure.19
Here we present experimental XA and X-ray emission (XE)
data of the parent hydrocarbon decalin and compare them toformer results for the perfluorocarbon PFD.19 A discussion of
the theoretically calculated absorption and emission spectra isalso presented. We reveal the energetic shift induced by theperfluoro eﬀect experimentally by XE measurements, which are
shown here to give complementary results to the XA spectra. In
addition, a systematic theoretical study for all stepwise fluorinateddecalin derivatives was performed with the aim to gain clear insight
into the mechanism of the perfluoro eﬀect and the MO character ofdecalin and PFD.

2 Experimental and theoretical details
2.1

Materials and methods

Perfluorodecalin (PFD) and Decalin were obtained from Alfa-Aeser
in a 50/50 cis/trans mixture with 495% purity for PFD and 498%
purity for Decalin. Resonant inelastic X-ray scattering (RIXS) andXE spectra at the Decalin carbon K-edge were recorded using aliquid microjet setup21,22 at the U41-PGM undulator beamline of
BESSY II at Helmholtz-Zentrum Berlin16 with a microjet diameterof around 14 mm. Detailed information about the end-station(LiXEdrom) is presented elsewhere.21,23 The RIXS and XE
measurements were performed using a Rowland-circle geometry
spectrometer with a grating of 5 m radius of curvature and1200 lines per mm. The detector, which is operated at a pressureof 10 9 mbar, consists of an MCP-stack, phosphorescent screen

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Paperand a CCD camera. The pressure in the experimental chamber isgenerally around 10 5 mbar. The beamline U41-PGM provides an
excitation energy bandwidth of 0.1 eV at the energy of 300 eV for
carbon excitations. The energy calibration and alignment of the RIXS
and XE spectra was performed using the elastic scattering features.
XA spectra were measured by using a transmission-type
liquid flow cell connected at soft X-ray undulator beamline
BL3U at the UVSOR-III Synchrotron facility.24 The details of theliquid flow cell are described elsewhere.25,26 The liquid cellconsists of four regions, which are separated by 100 nm thick
Si3N4 membranes. Soft X-rays under vacuum (region I) passthrough the buﬀer region filled with helium gas (region II) andthe liquid thin layer (region III) and finally reach a photodiodedetector in the last region filled with helium gas (region IV). A
liquid sample is sandwiched between two Si3N4 membranes
with pressed Teflon spacers set between the window frames ofthe membranes and can be substituted by other samples incombination with a tubing pump system. The thickness of theliquid layer can be controlled from 2000 to 20 nm by adjusting
the helium pressure in the regions II and IV. The energy
resolution of incident soft X-rays at C K-edge is set to 0.19 eV.
XA spectra are based on the Beer–Lambert law, ln(I0/I), where I0 and
I are the detection current through the cell without and withsamples, respectively. The energetic alignment of the spectrometer
was performed using CH4 gas and its absorption line.
2.2

Theoretical methods

The presented theoretical calculations were carried out with the
ORCA program package.15 Molecular geometry optimizations
were performed using the B3LYP27,28 density functional methodwith the def2-TZVP basis set.29,30 During the optimization calculations, the resolution of identity approximation31–35 was used
employing the def2-TZV/J basis set.36 Due to the chiral characterof the calculated molecules an optimization for each respective
configuration was performed. The electron population was calculated using the Löwdin population analysis formalism. Transitionenergies and moments for the K-edges of both cis and transconfigurations were calculated with time-dependent density functional theory (TD-DFT). The core-hole excited state calculations are
based on the computation of the dipole length and dipole velocity
formalisms. Additionally no intermolecular interaction effects inliquid phase are included. The presented X-ray emission spectra
were predicted with a one-electron approach, based on the above
described optimized geometries. K-edge absorption spectra wereobtained from the calculated transition moments from both chiralcontributions by applying a Gaussian type broadening of 0.8 eV.
The theory does not predict any significant diﬀerence between
the X-ray spectra of cis and trans forms of the molecule. All molecularorbitals are subsequently shown from the trans configuration.

3 Results and discussion
The experimental carbon K-edge XA spectrum of decalin(Fig. 1C) reveals two peaks at 287.2 eV and 288.7 eV followed
by a broad feature extending from 291 eV to 294 eV.

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The general spectral shape of the XA spectrum of decalin canalso be reproduced in shape and energetic position by theoreticalgas phase calculations for a single molecule employing the density
functional theory (DFT) algorithm for geometry optimizations and
TD-DFT for spectral calculations on single molecules (for details see
Theoretical methods). Nevertheless, the neglect of intermolecularinteractions inside the liquid probably leads to the diﬀerent intensity
ratios for the two peaks at 287.2 eV and 288.7 eV by comparing
theoretical and experimental data.
In Fig. 1C, the theoretical spectrum for all C sites (red line) was
obtained through the sum of the spectra for the non-equivalentcarbon sites. Additional calculations for the diﬀerent carbon atom
environments were derived in a similar manner as for PFD.19 Notethat the two diﬀerent carbon atom sites in decalin only diﬀer by the
number of bound hydrogen atoms. Eight carbon atoms are boundto two carbon and two hydrogen atoms as nearest neighbors (dC),while the two carbon atoms connecting the rings (sC) are bound to
three carbon atoms and one hydrogen atom as nearest neighbors.
Hence, these two carbon sites should have a significantly diﬀerent
chemical environment. The corresponding theoretical spectra wereobtained through the sum of the spectra for all dC and sC sites
respectively and are shown in Fig. 1C and depict surprisingly asimilar spectrum for dC and sC sites, in contrast to the findings
for PFD.19 In PFD the diﬀerence for the two carbon sites was
mainly attributed to the slight net charge diﬀerence for dC andsC atoms (0.26–0.27 for dC and 0.16 for sC).19 In contrast, fordecalin the negative net charge on the carbon atoms is quite
similar (0.21–0.23 for dC and 0.20 for sC), resulting in almost
identical spectra. Additionally, we take note of the change fromnegative net charge for decalin carbons to positive net charge for
PFD carbons, occurring due to the substitution of hydrogen tohighly electronegative fluorine.
The experimental carbon K-edge XE spectra (Fig. 1B) are ingood agreement with the calculated spectra (Fig. 1A). The
spectra in Fig. 1B reveal an excitation-energy dependence inthe range of 286.8–288.7 eV, where the high energy shoulder(b4) at 279.6 eV emission energy gains intensity. Additionally, thespectral structure remains unchanged for excitation energies
higher than 288.7 eV. This effect can be attributed to so-called
tail excitation and vibronic coupling.37,38
The XE spectrum of PFD reveals three peaks consisting of abroad low energy peak around 275 eV and two high energy
peaks.19 By comparing to XE spectra of rather simple fluoromethanes39 an influence of fluorine atoms to the high energy
features were shown.19 Subsequently the carbon K-edge emission
spectrum of CH4 should reveal similarities to decalin due to theabsence of fluorine atoms and the sp3-hybridized carbon character.
Indeed, CH4 shows one broad feature around 276.3 eV, which is anindicator for sp3 hybridized carbon.39 Furthermore, a glance at the
spectra of C2H6 and C3H8 reveals an additional shoulder comparedto the carbon XE spectra of CH4 at around 274.8 eV.40 This shoulder
can be attributed to C–C bond interactions and coincides with thedecalin b2 structure at 274.6 eV in this work.
As expected, the decalin spectrum is more complex than simple
fluorinated hydrocarbons, exhibiting a broad peak with two features
around 278 eV and small energetic shifts. Anyhow, due to theThis journal is © the Owner Societies 2015

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Fig. 1 Experimental and theoretical carbon K-edge X-ray emission (A, B) and X-ray absorption (C) data for decalin. Theoretically calculated data areshown for diﬀerent carbon sites. The highlighted edges in the RIXS spectra (B) indicate the excitation-energy dependent spectral features. Additional
information on the excitation processes for the diﬀerent spectroscopies is provided (D).

phenomenological similarity to simple hydrocarbons, we canassign b3 and b4 as sp3 hybridized carbon structures and theshoulder b2 as resulting from C–C bond interactions.
Fig. 2A and 3A show the experimental carbon K-edge XA and
XE spectra, respectively, for decalin and PFD and the calculated
spectra for these molecules as well as for the stepwise fluorinateddecalin derivatives (see also ESI†). The figures also visualize theshifts of the four main features for XA and the five main features
for XE spectra. As mentioned above, according to the dimensions of
the shifts for these features it is common to assign directly a s- or
p-character for the participating orbitals (B2–4 eV corresponds tos, B0–0.5 eV corresponds to p),11,12 where p is of out-of-plane anddiffuse (Rydberg-like) character, but not of anti-bonding character
like p*. This is summarized in Table 1. We note that the XE spectraof PFD and decalin are dominated by s type orbitals and that thefirst appreciable p contribution is in the XA region.
Features A and B2 are special due to their disappearance in the
spectra of PFD. All other calculated fluorocarbons show thesefeatures even though their intensity decreases with increasing
number of F atoms. Furthermore, these features do not havecorresponding PFD orbitals for the absorption process, but for theemission process. We additionally note that B2 only loses its dC
contribution to the spectrum, while the sC contribution remains of
the same intensity (see Fig. S1, ESI†).

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Features B2, G and D1 can only be assigned to both s- andp-orbital character since the observed energetic shift is in the range
known for strong s–p-hybridization. According to the relative highvalues of 1.3 eV and 1.4 eV for B2 and D1, respectively, a larger
contribution of s-character for these features can be assumed incomparison to G with a value of 0.9 eV for the energetic shift.
Complementary to the XA spectra, features d and e for the XE
spectra (Fig. 3A) require special attention. They do not exist in
decalin but appear upon fluorination. This coincides favorablywith the disappearance of the absorption features A and B2.
Simultaneously, both the XA features (A, B2) and the XE features(d, e) originate from similar MOs and we can assume a switchfrom unoccupied to occupied orbital region. The diﬀerences ofthe MOs have to be taken into account under the assumption of
the intrinsic diﬀerences between occupied and unoccupied
orbitals, like the electronic nodal planes and electron distribution. Accordingly, the change from unoccupied to occupied
orbitals (A to d and B2 to e) occurs due to the enormous numberof additional orbitals and the diﬀerent partial charge distributions based on the substitution of hydrogen by electronegative
fluorine. The stronger electronegativity results in a depopulation of most carbon orbitals (see the population analysis videsupra), giving dominance to fluorine signals in the XE spectra.19
The transformation of the previous pure carbon orbitals with

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Fig. 2 (A) Experimental (black lines) and calculated (blue lines) carbon K-edge X-ray absorption spectra for decalin and PFD as well as calculated spectra
for stepwise fluorinated decalin derivatives. Dashed lines indicate the shifts of the spectral features. (B) MOs for decalin and PFD corresponding to theshifting features are labeled in (A).

fluorine contribution can therefore lead to an energetic shift ofthe occupied orbitals due to the increase in fluorine character.
In addition to the orbital change, a s-shifting eﬀect isobserved. This s-shifting eﬀect is known for hydrocarbons, wherea C–C bond length increase is accompanied by a shift of s-features
to lower energies.41,42 The average C–C bond length was here
calculated to be 1.565 Å for PFD and 1.533 Å for decalin. Note,
the C–C bond length in partially fluorinated compounds is slightly
higher for bonds including fluorine substituted carbon atoms thanfor only hydrogen substituted carbon atoms (around 1.545–1.565 Å
vs. 1.529–1.534 Å). Hence, the s shifting has only impact where
fluorine substituted carbon atoms are involved. Consequently, theorbital change is strongly affected by s shifting, supporting andstrengthening the orbital rearrangement.
The aforementioned energetic shifts and assignments also
coincide with the observations of PFD RIXS measurements, inwhich the feature d is a mixture of sC and dC carbon sites and eof only dC carbon sites.19
As mentioned above, in a previous work19 we found that PFD
has a large HOMO–LUMO gap supposedly of importance for the

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chemical inertness and properties of PFD. By our present dataon decalin and the partially fluorinated hydrocarbons, we gain
insight into the mechanism behind this. For a precise estimation of
the gap, the energetic alignment of the different experimental
spectra is crucial. A detailed description on the alignment can befound under experimental methods. Our data supports a significant
increase of the gap for the last fluorination step (C10F26H2 to C10F28).
For this step, the gap increases by 1.2 eV due to the orbital change ofthe features A and B2 into the occupied orbital region additionallyto the systematic energy shift for these features. This increases therelative inertness according to the frontier orbital model43 andreveals the critical impact of the orbital change on the inertness ofthe perfluorinated molecule.
Additionally, parallels between the observed orbital change andmolecule enhancement methods through fluorine treatment
should be discussed.44,45 The observations are similar with respect
to the observed changes in the MO structure and the resulting
changes in chemical character.44–47 To enhance the mechanistic
understanding and involvement of the orbital change in thesemethods and molecules, further research on chain structured andThis journal is © the Owner Societies 2015

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Fig. 3 (A) Experimental (black lines) and calculated (blue lines) carbon K-edge X-ray emission spectra for decalin and PFD19 and calculated spectra for
stepwise fluorinated decalin derivatives. Dashed lines indicate the shifts of the spectral features. (B) MOs for decalin and PFD corresponding to the shifting
features are labeled in (A).

Table 1

Energetic shifts and derived MO character for the XA and XE features

XA characters and shifts

XE characters and shifts

FeatureEnergetic shift uponcomplete fluorination [eV]

Orbital character

FeatureEnergetic shift uponcomplete fluorination [eV]

Orbital character

A
B1
B2
G
D1
D2

1.8
0.3
1.3
0.9
1.4
0.1

s
p
Not distinguishable
Not distinguishable
Not distinguishable
p

a
b
g1
g2
g3
d
e

0.9
2.1
0.7
0.6
1.9
0.2
0.1

Not distinguishabless/not distinguishable
Not distinguishabless
Not distinguishable

more complex perfluoro compounds is in progress and will hopefully deliver a more general understanding of these findings.

4 Conclusions
In summary, we presented fundamental insight into the energetic
shift induced by fluorination, the so-called perfluoro eﬀect, and aThis journal is © the Owner Societies 2015

comprehensive picture of the electronic structure of decalin as theparent hydrocarbon molecule for the recently investigatedperfluorodecalin19 based on XA, XE and RIXS spectroscopic
data. In addition, DFT calculations for decalin, perfluorodecalinand stepwise fluorinated decalin derivatives were performed. We
observed a change in occupancy of MOs occurring for the
fluorinated hydrocarbons when reaching complete fluorinationin PFD. This MO alteration may be one of the main reasons forPhys. Chem. Chem. Phys., 2015, 17, 18337--18343 | 18341

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the chemical and biological inertness of the ring-shaped perfluorodecalin compared to decalin and the corresponding partiallyfluorinated hydrocarbons.3,4 Interestingly, the orbital change
assigned to the A and B2 feature in the XA spectra could also
be observed in the XE spectra for the features d and e in acomplementary way. To the best of our knowledge, the observability of the perfluoro eﬀect via XE spectra was confirmed for the
first time, and the orbital change originating from unoccupied
decalin to occupied PFD MOs was also discussed in relation to
the well-known high electronegativity of fluorine atoms. Hence,the validity of this concept and its extension to linear and also
larger perfluoro systems is of particular interest for a better
understanding of the special properties of perfluoro compounds
and their application development.

Acknowledgements
This work was supported by the Helmholtz-Gemeinschaft via
the young investigator fund VH-NG-635. Part of this work was
financially supported by the European Research Council grantNo. 279344. Tristan Petit acknowledges the Alexander von
Humboldt foundation for financial support. Kaan Atak would
like to acknowledge the financial support of the EinsteinFoundation Berlin for the postdoctoral scholarship in the Aziz
team. This work is supported by JSPS Grants-in-Aid for Scientific
Research (No. 26248010). We acknowledge the staﬀ members of
the UVSOR-III Synchrotron facility for their kind support.

References
1 J.-A. Ma and D. Cahard, Chem. Rev., 2004, 104, 6119–6146.
2 Selective Fluorination in Organic and Bioorganic Chemistry,ed. J. T. Welch, American Chemical Society, Washington,
DC, 1991, vol. 456.
3 M. A. Hamza, G. Serratrice, M. J. Stebe and J. J. Delpuech,
J. Am. Chem. Soc., 1981, 103, 3733–3738.
4 A. M. A. Dias, M. Freire, J. A. P. Coutinho and I. M. Marrucho,
Fluid Phase Equilib., 2004, 222–223, 325–330.
5 K. C. Lowe, Blood Rev., 1999, 13, 171–184.
6 M. C. Papo, P. R. Paczan, B. P. Fuhrman, D. M. Steinhorn,
L. J. Hernan, C. L. Leach, B. A. Holm, J. E. Fisher and
B. A. Kahn, Crit. Care Med., 1996, 24, 466–474.
7 P. R. Lyunch, L. J. Krasner, T. Vinciquerra and T. H. Shaﬀer,
Undersea Biomed. Res., 1989, 16, 275–281.
8 M. Velikay, A. Wedrich, U. Stolba, P. Datlinger, Y. Li and
S. Binder, Am. J. Ophthalmol., 1993, 116, 565–570.
9 F. Bottoni, G. Bailo, P. Arpa, A. Prussiani, M. Monticelli and
V. de Molfetta, Ophthalmic Surg., 1994, 25, 365–373.
10 P. Decleva, M. Stener, D. M. P. Holland, A. W. Potts and
L. Karlsson, J. Phys. B: At., Mol. Opt. Phys., 2007, 40, 2939.
11 C. R. Brundle, M. B. Robin, N. A. Kuebler and H. Basch,
J. Am. Chem. Soc., 1972, 94, 1451–1465.
12 C. R. Brundle, M. B. Robin and N. A. Kuebler, J. Am. Chem.
Soc., 1972, 94, 1466–1475.

18342 | Phys. Chem. Chem. Phys., 2015, 17, 18337--18343

PCCP

13 M. B. Robin, I. Ishii, R. McLaren and A. P. Hitchcock,
J. Electron Spectrosc. Relat. Phenom., 1988, 47, 53–92.
14 I. Ishii, R. McLaren, A. P. Hitchcock, K. D. Jordan, Y. Choiand M. B. Robin, Can. J. Chem., 1988, 66, 2104–2121.
15 F. Neese, Wiley Interdiscip. Rev.: Comput. Mol. Sci., 2012, 2,
73–78.
16 C. Jung, F. Eggenstein, S. Hartlaub, R. Follath, J. S. Schmidt,
F. Senf, M. R. Weiss, T. Zeschke and W. Gudat, Nucl.
Instrum. Methods Phys. Res., Sect. A, 2001, 467–468(Part 1),
485–487.
17 M. Nagasaka, H. Yuzawa, T. Horigome, A. P. Hitchcock and
N. Kosugi, J. Phys. Chem. C, 2013, 117, 16343–16348.
18 F. Gel’mukhanov and H. Ågren, Phys. Rep., 1999, 312,
87–330.
19 T. Brandenburg, M. Agåker, K. Atak, M. Pflüger, C. Schwanke,
T. Petit, K. M. Lange, J.-E. Rubensson and E. F. Aziz, Phys.
Chem. Chem. Phys., 2014, 16, 23379–23385.
20 E. P. Wesseler, R. Iltis and L. C. Clark Jr., J. Fluorine Chem.,
1977, 9, 137–146.
21 K. M. Lange, R. Könnecke, S. Ghadimi, R. Golnak, M. A.
Soldatov, K. F. Hodeck, A. Soldatov and E. F. Aziz, Chem.
Phys., 2010, 377, 1–5.
22 K. M. Lange, M. Soldatov, R. Golnak, M. Gotz, N. Engel,
R. Könnecke, J.-E. Rubensson and E. F. Aziz, Phys. Rev. B:
Condens. Matter Mater. Phys., 2012, 85, 155104.
23 K. M. Lange, R. Könnecke, M. Soldatov, R. Golnak, J.-E.
Rubensson, A. Soldatov and E. F. Aziz, Angew. Chem., 2011,
123, 10809–10813.
24 T. Hatsui, E. Shigemasa and N. Kosugi, in AIP Conference
Proceedings, AIP Publishing, 2004, vol. 705, pp. 921-924.
25 M. Nagasaka, T. Hatsui, T. Horigome, Y. Hamamura andN. Kosugi, J. Electron Spectrosc. Relat. Phenom., 2010, 177,
130–134.
26 M. Nagasaka, K. Mochizuki, V. Leloup and N. Kosugi,
J. Phys. Chem. B, 2014, 118, 4388–4396.
27 A. D. Becke, Phys. Rev. A: At., Mol., Opt. Phys., 1988, 38,
3098–3100.
28 A. D. Becke, J. Chem. Phys., 1993, 98, 5648–5652.
29 A. Schäfer, H. Horn and R. Ahlrichs, J. Chem. Phys., 1992, 97,
2571–2577.
30 F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys., 2005,
7, 3297.
31 E. J. Baerends, D. E. Ellis and P. Ros, Chem. Phys., 1973, 2,
41–51.
32 B. I. Dunlap, J. W. D. Connolly and J. R. Sabin, J. Chem.
Phys., 2008, 71, 3396–3402.
33 O. Vahtras, J. Almlöf and M. W. Feyereisen, Chem. Phys.
Lett., 1993, 213, 514–518.
34 K. Eichkorn, O. Treutler, H. Öhm, M. Häser and R. Ahlrichs,
Chem. Phys. Lett., 1995, 240, 283–290.
35 K. Eichkorn, F. Weigend, O. Treutler and R. Ahlrichs, Theor.
Chem. Acc., 1997, 97, 119–124.
36 F. Weigend, Phys. Chem. Chem. Phys., 2006, 8, 1057.
37 P. Skytt, J. Guo, N. Wassdahl, J. Nordgren, Y. Luo andH. Ågren, Phys. Rev. A: At., Mol., Opt. Phys., 1995, 52,
3572–3576.

This journal is © the Owner Societies 2015

View Article Online

Published on 18 June 2015. Downloaded by OKAZAKI NATIONAL RESEARCH INST on 09/07/2015 10:56:50.

PCCP

38 J. Guo, X-Rays in Nanoscience: Spectroscopy, Spectromicroscopy,
and Scattering Techniques, John Wiley & Sons, 2011.
39 P. Glans, R. E. L. Villa, Y. Luo, H. Agren and J. Nordgren,
J. Phys. B: At., Mol. Opt. Phys., 1994, 27, 3399.
40 R. Manne, J. Chem. Phys., 1970, 52, 5733–5739.
41 A. P. Hitchcock, D. C. Newbury, I. Ishii, J. Stöhr, J. A. Horsley,
R. D. Redwing, A. L. Johnson and F. Sette, J. Chem. Phys.,
1986, 85, 4849–4862.
42 F. Sette, J. Stöhr and A. P. Hitchcock, J. Chem. Phys., 1984,
81, 4906–4914.

This journal is © the Owner Societies 2015

Paper

43 K. Fukui, T. Yonezawa and H. Shingu, J. Chem. Phys., 1952,
20, 722–725.
44 A. Tressaud, E. Durand, C. Labrugère, A. P. Kharitonov andL. N. Kharitonova, J. Fluorine Chem., 2007, 128, 378–391.
45 R. G. Haverkamp and B. C. C. Cowie, Surf. Interface Anal.,
2013, 45, 1854–1858.
46 J. Guo, P. Resnick, K. Efimenko, J. Genzer and J. M. DeSimone,Ind. Eng. Chem. Res., 2007, 47, 502–508.
47 L. J. Gamble, B. Ravel, D. A. Fischer and D. G. Castner,
Langmuir, 2002, 18, 2183–2189.

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