Published on 19 July 2013. Downloaded by State University of New York at Stony Brook on 30/10/2014 04:31:01.
RSC Advances
View Article Online
PAPER
View Journal | View Issue
Electron affinity of phenanthrene and ion core structure
of its anion clusters
Cite this: RSC Advances, 2013, 3,
17143
Sang Hak Lee,a Namdoo Kim,a Dong Gyun Haa and Jae Kyu Song*b
We studied anion clusters of phenanthrene, Pnn2 (n = 1–8), by mass distributions, photoelectron spectra,
and theoretical calculations to determine the electron affinity of phenanthrene and the ion core structures
of Pnn2. The electron affinity of phenanthrene was determined to be 0.12 eV. The parallel-displaced
structures with a fully delocalized excess electron over the entire phenanthrene moieties, which were
Received 9th July 2013,
Accepted 19th July 2013
obtained as stable geometries in the theoretical calculations, implied the presence of dimeric and trimeric
ion cores in Pn22 and Pn32, respectively. For the tetramer and pentamer, photoelectron spectra with broad
features and shoulders suggested the coexistence of ion cores. The magic number in the mass distributions
DOI: 10.1039/c3ra43498b
www.rsc.org/advances
and the unusual vertical detachment energy in the hexamer indicated the formation of a half-filled
solvation shell.
1. Introduction
Non-bonding interactions, such as hydrogen bonding and p–p
stacking interactions, work effectively on the properties and
the structures of biomolecules and molecular crystals.1–3 The
structures of DNA and RNA are innately conserved by such
interactions.4–6 These interactions are also important for the
efficiency of electron transport in organic light emitting
diodes.7–9 Thus polycyclic aromatic hydrocarbon (PAH) molecules have been extensively investigated in the condensed
phase and gas phase, so as to understand the non-bonding
interactions related to the electrical and optical properties.10
However, these interactions have been studied mostly in
neutral and cationic states,11,12 whereas the interactions in
anionic states have been rarely reported. Studies of the
intermolecular interactions of prototypical molecules like
phenanthrene (Pn) will help to understand non-bonding
interactions in anionic states. Therefore, the ion core
structures of aromatic anion clusters are worth being
examined in detail because intermolecular interactions are at
play in the ion core structures. For example, a monomeric
anion was consistently observed in the small sizes of
naphthalene anion clusters,13,14 while several ion cores were
found in anthracene and pyrene anion clusters.15–18
The electron binding of a molecule is another fundamental
property of the molecule, and plays a critical role in the
prediction of the efficiency of organic electronics.19 Thus the
electron affinity (EA) of the PAH molecule, which is a building
block of the organic crystals and organic light emitting diodes,
a
Department of Chemistry, Seoul National University, Seoul 151-747, Korea
Department of Chemistry, Kyung Hee University, Seoul 130-701, Korea.
E-mail: jaeksong@khu.ac.kr; Fax: +82 (0)2 966 3701
b
This journal is ß The Royal Society of Chemistry 2013
has been investigated using experimental and theoretical
methods. In general, the EA of PAH molecules increases with
an increase in the molecular size. However, the EAs of a few
PAHs cannot clearly be explained as a function of the
molecular size. For example, EA increases with an expansion
of the p-orbital system; benzene (21.12 eV, vertical EA, EAv),20
naphthalene (20.19 eV, EAv),20 anthracene (0.54 eV, adiabatic
EA, EAa),15,21–23 and tetracene (1.05 eV, EAa),24 whereas pyrene
(0.45 eV, EAa) has a lower value than anthracene.17,18,25 In
addition, the EA of Pn has not been confirmed, as previous
studies have reported differing results. Recently, a negative
value (20.01 eV) was estimated by extrapolation of the EAa of
clusters with microsolvation correction.26 On the other hand, a
positive value (0.31 eV, EAv) was also suggested by the electron
capture detection method.27,28
In this study, we present the direct measurement of the EA
of Pn. The ion core structures in anion clusters of Pn were also
examined in order to investigate the non-bonding interactions
in the anion states of PAHs. Several ion core structures
(monomeric, dimeric, trimeric, and tetrameric cores) were
observed, while the coexistence of ion cores was identified in
tetramer and pentamer anions. The magic number in the mass
distributions revealed the completion of a half-filled solvation
shell at hexamer anions.
2. Experimental
The details of the anion mass spectrometer and of the
photoelectron spectrometer have been reported elsewhere.16
A brief explanation of the apparatus employed in this work is
presented here. The pulsed molecular beam was generated by
expanding Pn vapor (160 uC), seeded in Ar carrier gas, through
RSC Adv., 2013, 3, 17143–17149 | 17143
View Article Online
Published on 19 July 2013. Downloaded by State University of New York at Stony Brook on 30/10/2014 04:31:01.
Paper
a pulsed valve operated at 10 Hz with a stagnation pressure of
y7 atm. The anion clusters were produced by electron impact
(400 eV, 300 mA) in a supersonic expansion resulting in slow
secondary electrons. The anion clusters were extracted to a
Wiley–McLaren-type 1.8 m time-of-flight mass spectrometer.
The resolution of the mass spectrometer (M/DM) was about
200. The anions of interest were selected to enter the
photoelectron spectrometer by a mass gate. The kinetic
energies of the selected anions were decelerated to less than
20 eV by a potential switch, which effectively reduced Doppler
broadening in the photoelectron spectra. The photoelectron
spectra were obtained at various wavelengths such as 1064,
740, and 532 nm using an Nd:YAG laser and a dye laser. The
full width at half maximum energy resolution of the magneticbottle-type photoelectron spectrometer was about 0.05 eV at 1
eV electron kinetic energy. The photoelectron spectrometer
was calibrated against the photoelectron spectrum of O22. The
laser power was kept unfocused at 5 mJ pulse21 cm22 to
reduce the multiphoton effect.
RSC Advances
Fig. 2 Photoelectron spectrum of the phenanthrene monomer anion, Pn12,
obtained at 1064 nm. Black solid bar indicates the vertical detachment energy
(VDE) of Pn12 and gray solid bars denote the fundamental vibration of the
totally symmetric C–H wagging mode (A1, 0.18 eV, 1431 cm21). EBE denotes the
electron binding energy. The inset shows the vibrational motion of the totally
symmetric C–H wagging mode.
3. Results
A typical mass distribution of Pnn2 is presented in Fig. 1. An
anomaly in ion intensities is consistently found at n = 6, under
various experimental conditions. Since the intensity anomalies
of ion clusters often provide an insight into the nature of
solvation shell structures,16,29,30 the ‘‘magic number’’ at n = 6
suggests the formation of a solvation shell in Pnn2. The
monomer anion is barely discernible in Fig. 1 because this
mass distribution is obtained at conditions optimized for
larger clusters. However, the monomer anion, Pn12, is clearly
observed in the mass distribution chosen to enhance smaller
clusters (inset of Fig. 1).
Fig. 1 Mass distribution of phenanthrene anion clusters, Pnn2, chosen to
enhance larger clusters. The magic number is observed at n = 6. The inset shows
another mass distribution chosen to optimize smaller clusters such as a
monomer anion. Asterisks indicate Ar adducts such as Pn12Ar1 and Pn12Ar2.
17144 | RSC Adv., 2013, 3, 17143–17149
Recently, the EAa of Pn was reported as a negative value
(20.01 eV), which was estimated by the extrapolation of the
EAa of (Pn1)(H2O)n in addition to the absence of the monomer
anion in the mass distribution.26 However, Pn12 observed in
our mass distributions suggests that Pn has a positive EAa.
Moreover, the vertical detachment energy (VDE), which
corresponds to the band maximum in the photoelectron
spectrum, is a positive value of 0.12 eV in the photoelectron
spectrum of Pn12 (Fig. 2). The partially resolved spectral
feature in the photoelectron spectrum is identified as the
vibrational mode of neutral Pn (C–H wagging mode, A1, 0.18
eV, 1431 cm21).31,32 Therefore, VDE (0.12 eV) is assigned as the
0–0 transition energy and thus represents the EA of Pn.
Photoelectron spectra of Pnn2 (n = 1–4) obtained at 1064
nm show that the VDEs are 0.27, 0.48, and 0.55 eV for Pn22,
Pn32, and Pn42, respectively (Fig. 3). Although the overall
spectral shape appears to be similar at first glance, a careful
inspection reveals that the spectral shapes possess several
different features. For example, the intensity of the vibrational
mode appears to change in Pn22 and Pn32. The spectral shape
of Pn42 is also different from those of others, where the overall
shape is much broader and the adjacent peak (0.69 eV) has a
similar intensity to that of VDE (0.55 eV). The spectral features
of photoelectron spectra contain information relating to the
ion core structures of clusters,16,29,30 while the spectral feature
is also influenced by an autodetachment process with a strong
wavelength dependence.17 Photoelectron spectra of Pnn2 (n =
2–8) are also obtained at other wavelengths, such as 740 and
532 nm (Fig. 4), to determine whether the unique spectral
features originate from ion core structures or autodetachment
processes. The spectral shape of Pn42 at 740 nm is also
structureless and broad, differing from the well-resolved
spectra of Pn22 and Pn32 at 740 nm. Therefore, the broad
This journal is ß The Royal Society of Chemistry 2013
View Article Online
Published on 19 July 2013. Downloaded by State University of New York at Stony Brook on 30/10/2014 04:31:01.
RSC Advances
Paper
spectra of Pn42 result from the ion core structures rather than
from the autodetachment process. In the photoelectron
spectra of Pn52, the spectral feature begins with a shoulderlike origin whose energy is smaller than the VDE of Pn42. The
possibility of an autodetachment process is also ruled out for
the shoulder because both spectra at 740 and 532 nm show
similar intensities of the shoulder. In this regard, the ion cores
are responsible for the shoulder in Pn52. The VDE of Pn62 is
smaller than that of Pn52, while VDEs increase slowly from
Pn62 to Pn82. The vibrational structures in the photoelectron
spectra of larger clusters (n ¢ 6) are less-resolved because the
vibrational progressions become smeared out with increasing
cluster size. Photoelectron spectra at 532 nm are virtually
identical to those at 740 nm, except for the occurrence of
slightly broader spectral shapes due to the high kinetic energy
imparted to photoelectrons.
4. Theoretical calculations
Fig. 3 Photoelectron spectra of phenanthrene anion clusters, Pnn2 (n = 1–4), as
measured by photodetachment at 1064 nm. EBE denotes the electron binding
energy.
Fig. 4 Photoelectron spectra of phenanthrene anion clusters, Pnn2 (n = 2–8), as
measured by photodetachment at 740 (left) and 532 nm (right). EBE denotes
the electron binding energy.
This journal is ß The Royal Society of Chemistry 2013
Density functional theory calculations were carried out using
the GAUSSIAN package to obtain optimized geometries of Pn
anion clusters.33 All the stable structures were determined
using analytical gradients with full optimization. The frequencies of the optimized geometries were also calculated in order
to ensure that the structures represented the stable points on
the potential energy surface. The excess electron was confirmed to be in a valence p* orbital, which is the lowest
unoccupied molecular orbital (LUMO) of the Pn neutral and
singly occupied molecular orbital (SOMO) of the Pn anion. The
geometry difference between the anion and the neutral of the
Pn moiety (not shown) was closely related to the C–H wagging
mode (Fig. 2), which explains the predominant vibrational
progression in the photoelectron spectra. The stable geometry
of Pn22, obtained at the level of B3LYP/6-31++G**, is paralleldisplaced (PD) and its excess electron is evenly delocalized
over two Pn moieties (Fig. 5), implying a dimeric ion
structure.2
For small aromatic hydrocarbon anions, the interaction of
p electrons with the negative charge is repulsive, whereas the
hydrogen atoms of the neutral aromatic hydrocarbons
undergo p–hydrogen bonding with the anion. Thus the
naphthalene–benzene and naphthalene–naphthalene anion
complexes have T-shaped geometries.14 On the other hand, the
delocalization of an excess electron over the large PAH
molecules reduces the charge-induced effects. In addition,
the enhanced stacking interaction in large PAH anion dimers
is strong enough to compensate for the repulsion between the
negatively charged aromatic rings. The stacking interactions
are even larger than the p–hydrogen bonding, as in the cases
of PD anthracene dimer and pyrene dimer anions.15,17
Therefore, the PD geometry of Pn22 results from the molecular
size effect, which influences the main intermolecular interactions and determines the stable geometries of PAH anion
dimers.
RSC Adv., 2013, 3, 17143–17149 | 17145
View Article Online
Published on 19 July 2013. Downloaded by State University of New York at Stony Brook on 30/10/2014 04:31:01.
Paper
Fig. 5 (a) The most stable geometry of Pn22. (b) The most stable geometry of
Pn32. (c) The most stable geometry of Pn42.
Calculations of Pn32 revealed the double-parallel-displaced
(d-PD) geometry to be the most stable form. An excess electron
is delocalized nearly equally over three Pn moieties, suggesting
a trimeric ion core. The geometry and electron distribution of
Pn32 is quite similar to that of anthracene trimer anions.15,16
The stable geometry of Pn42 is crossed-parallel-displaced (cPD). An excess electron is also equivalently delocalized, which
implies that the most stable tetramer has a tetrameric ion
core. For calculations of Pn42, a smaller basis set (6-31+G*)
was employed in order to obtain reliable results with a
moderate amount of computational cost. Although the
coexistence of ion cores is suggested by the photoelectron
spectra, we could not find other reliable geometries, presumably because Pn42 is too large to optimize all possible
geometries by density functional theory calculations.
5. Discussion
5.1 Electron affinity of phenanthrene
The expansion of p-orbitals in the molecular framework
changes the EAs of aromatic complexes. Small aromatic
hydrocarbons have negative EAs, as in the case of benzene
with its EAv of 21.12 eV.20 Upon expansion of p-orbital systems
in PAH molecules, the molecular framework leads to delocalization of an excess electron, which increases the EAs of PAH
molecules. The EAs of naphthalene (Np) and anthracene (An)
are 20.19 (EAv) and 0.54 eV (EAa), respectively.20–23 However,
the EAa of pyrene (Py) is smaller (0.45 eV) than that of An,17,25
although the molecular framework of Py is larger than that of
An, which implies that the evolution of EA cannot be explained
simply by the number of p electrons in PAH molecules. The EA
17146 | RSC Adv., 2013, 3, 17143–17149
RSC Advances
of Pn, which has the same molecular formula (C14H10) as An,
has been controversial. The extrapolated value (20.01 eV, EAa)
from the clusters was much different from a positive value
(0.31 eV, EAv) obtained by the electron capture detection
method.26–28 The theoretical calculations also provided
unclear results. The EAa was negative (20.034 eV) prior to
zero-point energy correction, whereas it becomes positive
(0.128 eV) after zero-point energy correction.26 In addition,
other positive EAa values were reported (0.14 and 0.15 eV)
using empirical scaling of the LUMO energies of a large
number of PAHs.34 We note that the small yet unmistakable
intensity of Pn12 is observed in the mass distributions (Fig. 1).
The low ion intensity of Pn12, despite the expected abundance
of its counter neutrals, implies that electron attachment to Pn
is hindered due to its low EA. Therefore, the small value of EA
(0.12 eV) explains the low intensity of Pn12 in the mass
distributions. In addition, the experimental value (0.12 eV) is
in agreement with the theoretical value (0.128 eV) obtained by
the zero-point energy correction.26 It is also noted that the 0–1
transition of the A1 mode (0.30 eV in Fig. 2) happens to match
the reported EA (0.31 eV) obtained by the electron capture
detection.27,28
The EA of Pn is smaller than that of An, despite their same
molecular formula. Both molecules originate from the reaction
of Np and butadiene, however the molecular orbitals differ
due to the characteristic reaction position of butadiene with
respect to Np. Accordingly, the orbital energy levels, such as
HOMO and LUMO, are not identical, thus accounting for the
larger ionization energy and smaller EA of Pn relative to An.
5.2 Coexistence of ion core structures in Pnn2 (n = 4, 5)
The unusual photoelectron spectra of Pnn2 suggest the change
of the ion core structures with increasing cluster size. In order
to understand the ion core structures of Pnn2, those of Ann2
are examined because p–p stacking interactions are assumed
to be predominant in Pnn2 as in Ann2.15,16 The ion cores of
Ann2 changed from monomeric to dimeric and trimeric, from
n = 1 to 3. In addition, the coexistence of two ion cores was
observed for n = 4. When the solvation shell was half-filled, the
ion core was restored to the monomeric one at n = 5. Then, the
monomeric form was the major ion core between the halffilled and completely-filled first solvation shell. Likewise, the
ion core seems to undergo multiple switching in Pnn2, i.e., the
monomeric, dimeric, and trimeric ion core in the monomer,
dimer, and trimer, respectively, as suggested by the theoretical
calculations (Fig. 5). In addition, the coexistence of ion cores is
ruled out at n = 2 and 3, because the photoelectron spectra
obtained at 740 nm are deconvoluted by a single series of
peaks having an equal energy spacing of the C–H wagging
mode (Fig. 6). On the other hand, an inclusion of another lowenergy band turns out to be more appropriate at n = 4 and 5,
which suggests the coexistence of ion cores. In other words,
the coexistence of ion cores changes the shapes of the
photoelectron spectra because the VDE of each ion core is
not identical, i.e., one with a smaller VDE and the other with a
larger VDE, as in the previous reports of anthracene tetramer
anions and pyridine tetramer anions.15,35
A few ion cores can be formed during cluster anion
generation when the relative stabilities are comparable and
This journal is ß The Royal Society of Chemistry 2013
View Article Online
Published on 19 July 2013. Downloaded by State University of New York at Stony Brook on 30/10/2014 04:31:01.
RSC Advances
Paper
ion core (Fig. 5a). Thus the dimeric ion core might be
facilitated by the reduction of the intermolecular plane
distance in one parallel-displaced unit, while the other unit
(two molecules) serves as solvent. The relative stability of two
ion cores is estimated by the intensity of each ion core in the
photoelectron spectra, with the assumption that the absorption coefficients are not different to one other. The ion core
with the larger VDE, which is assigned as the tetrameric core,
shows a larger intensity in the deconvoluted photoelectron
spectrum (Fig. 6), implying that the tetrameric core is
predominant in Pn42. The large intensity indicates that the
tetrameric core is more stable than the dimeric one, which
agrees with the theoretical calculations in that the tetrameric
one is optimized as the most stable form.
Similarly, the deconvoluted photoelectron spectrum of Pn52
indicates the coexistence of ion cores. Thus the evolution of
VDEs is examined to obtain an insight into the possible ion
cores in Pn52 because we do not have a clue about structural
information for Pn52 at this point. The VDE values are
reasonably connected to the monomeric and trimeric ion
cores. The ion cores in Pn52 are totally different from those in
Pn42, i.e., (Pn2)2(Pn2) and (Pn4)2 in Pn42 but (Pn1)2(Pn4) and
(Pn3)2(Pn2) in Pn52. Interestingly, the even numbers of solvent
molecules are a common feature; zero solvent molecule in
(Pn4)2(Pn0), two solvent molecules in (Pn2)2(Pn2), two solvent
molecules in (Pn3)2(Pn2), and four solvent molecules in
(Pn1)2(Pn4). Therefore, an even number of solvent molecules
seems to be at play in the anion cluster systems. In other
words, the ion–solvent interactions with an even numbers of
solvent molecules seem to be effective, possibly due to the
symmetric geometries.18,24
5.3 Closure of solvation shell in Pn62
Fig. 6 Photoelectron spectra of phenanthrene anion clusters, Pnn2 (n = 2–8),
measured by photodetachment at 740 nm. The deconvolution of the spectra by
a set of Gaussian functions indicates the ion core structures, which are
represented by different colors; monomeric ion core (dark gray), dimeric one
(white), trimeric one (gray), and tetrameric one (dark yellow-green). Connected
lines denote the same kinds of ion core structures. EBE denotes the electron
binding energy.
the barriers to separate the ion cores are significant compared
to the internal energy. The theoretical calculations show a
tetrameric ion core in Pn42 with c-PD geometry. However,
another ion core is suggested in the photoelectron spectra of
Pn42, which is estimated by the evolution of VDEs. Generally,
the increment of VDE becomes smaller with increasing cluster
size due to the reduction of the effective electrostatic
interaction between the anion core and the solvent. In this
regard, the VDE of the low-energy band at n = 4 shows a
reasonable line connection to the dimeric ion cores (Fig. 6),
suggesting that another ion core is the dimeric one,
(Pn2)2(Pn2). In addition, the geometry of the tetrameric core
contains a clue as to the possible geometry of the dimeric one.
The c-PD geometry consists of two PD dimer units (Fig. 5c),
both of which are similar to the stable geometry of the dimeric
This journal is ß The Royal Society of Chemistry 2013
In contrast to Pn42 and Pn52, the spectral feature of Pn62
suggests a single ion core because the photoelectron spectrum
is deconvoluted with a single progression of the C–H wagging
mode as found in Pn22 (Fig. 6). In addition, the VDE of Pn62 is
smaller than that of Pn52. Another unique feature of Pn62 is
the magic number in the mass distributions. Since the magic
number indicated the half-filling of the solvation shell in
Ann2,15,16 the half-shell closure is suggested in Pnn2. The VDE
of Pn62 connects a line to the VDEs of the dimeric ion core
(Fig. 6), which indicates the recurrence of the dimeric ion core,
assisted by the four solvent molecules. A common feature of
the half-shell closure in An52 and Pn62 is the four solvent
molecules, which solvate most effectively the ion cores like
An12 and Pn22, respectively, although the values of magic
numbers are not identical. In addition, the increase in VDEs is
quite small from Pn62 to Pn82 and the spectral features of
Pn72 and Pn82 indicate that the ion cores do not differ from
those of Pn62. In general, a successive solvent stabilizes the
cluster anion less efficiently due to reduced interactions
between the anion core and solvents. The solvation effect
decreases more noticeably after the shell-closure because of
the increased intermolecular distance and the shielding of the
ionic charge. Therefore, the increment of the VDEs, which is
clearly reduced from n = 6, supports the (half-) filling of a first
solvation shell at n = 6.
RSC Adv., 2013, 3, 17143–17149 | 17147
View Article Online
Published on 19 July 2013. Downloaded by State University of New York at Stony Brook on 30/10/2014 04:31:01.
Paper
Despite the same molecular formula for Pn and An, the halfshell closures are not observed at the same cluster size. In
other words, the magic numbers are found by the shell closure
at An52 and Pn62. The main difference comes from the
structures of molecules that serve as the solvents. Compared to
the linear-type structure of An, Pn is regarded as a nonlineartype molecule. Thus the close-packing of the four Pn solvent
molecules might be less favorable than that for An.15,18 In this
regard, the four solvents solvate the large-sized dimer ion in
Pnn2 more effectively than the monomer ion, whereas the
monomer ion can be well solvated by closely-packed four
solvents in Ann2.
6. Conclusions
In this study, the EA of Pn is found to be 0.12 eV. Despite the
same molecular formula of Pn and An, the EA is much
different due to the characteristic orbital interactions. The
dimeric and trimeric ion cores are found in Pn22 and Pn32
with PD and d-PD structures, respectively, by density functional theory calculations. The p–p stacking interaction turns
out to be a structure-determining interaction in Pn22 and
Pn32, as in An22 and An32. The coexistence of ion cores
observed in Pn42 and Pn52 is related to the number of solvent
molecules because the symmetric geometries with even
numbers of solvent molecules stabilize the anion cluster
systems more effectively. The magic number at n = 6 in mass
distributions indicates the closure of the half-solvation shell
with the dimeric ion core and four solvent molecules. After
closing the half-solvation shell, the dimeric ion core is
predominant. Although the p–p stacking interaction is a
structure-determining interaction in Pnn2, as in Ann2, the
cluster size of the half-shell is not the same, which is
attributed to the molecular structure difference.
Acknowledgements
This research was supported by Basic Science Research
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education, Science and
Technology (NRF-2012R1A1A2039882). This work was also
supported by the National Research Foundation of Korea
Grant funded by the Korean Government (MEST, NRF-2009C1AAA001-0092939). This work was also supported by the
National Research Foundation of Korea through the Star
Faculty Program (2005-0093840) and the Global Frontier R&D
Program on Center for Multiscale Energy System (20110031567). The authors thank Professor Seong Keun Kim for
his stimulating discussion of the content.
References
1 C. Desfrancois, S. Carles and J. P. Schermann, Chem. Rev.,
2000, 100, 3943.
17148 | RSC Adv., 2013, 3, 17143–17149
RSC Advances
2 A. D. Buckingham, P. W. Fowler and J. M. Hutson, Chem.
Rev., 1988, 88, 963.
3 E. A. Meyer, R. K. Castellano and F. Diederich, Angew.
Chem., Int. Ed., 2003, 42, 1210.
4 C. R. Calladine and H. R. Drew, J. Mol. Biol., 1986, 192, 907.
5 J. Sponer, H. A. Gabb, J. Leszczynski and P. Hobza, Biophys.
J., 1997, 73, 76.
6 C. A. Hunter, J. Mol. Biol., 1993, 230, 1025.
7 J. C. Deaton, D. W. Place, C. T. Brown, M. Rajeswaran and
M. E. Kondakova, Inorg. Chim. Acta, 2008, 361, 1020.
8 L. S. Sapochak, P. E. Burrows, D. Garbuzov, D. M. Ho, S.
R. Forrest and M. E. Thompson, J. Phys. Chem., 1996, 100,
17766.
9 L. S. Sapochak, A. Padmaperuma, N. Washton, F. Endrino,
G. T. Schmett, J. Marshall, D. Fogarty, P. E. Burrows and S.
R. Forrest, J. Am. Chem. Soc., 2001, 123, 6300.
10 T. Shida and S. Iwata, J. Am. Chem. Soc., 1973, 95, 3473.
11 H. J. Neusser and H. Krause, Chem. Rev., 1994, 94, 1829.
12 H. Saigusa and E. C. Lim, J. Phys. Chem., 1994, 98, 13470.
13 J. K. Song, S. Y. Han, I. H. Chu, J. H. Kim, S. K. Kim, S.
A. Lyapustina, S. J. Xu, J. M. Nilles and K. H. Bowen, J.
Chem. Phys., 2002, 116, 4477.
14 S. H. Lee, J. H. Kim, I. Chu and J. K. Song, Phys. Chem.
Chem. Phys., 2009, 11, 9468.
15 J. K. Song, N. K. Lee and S. K. Kim, Angew. Chem., Int. Ed.,
2003, 42, 213.
16 J. K. Song, N. K. Lee, J. H. Kim, S. Y. Han and S. K. Kim, J.
Chem. Phys., 2003, 119, 3071.
17 J. H. Kim, S. H. Lee and J. K. Song, J. Chem. Phys., 2009, 130,
124321.
18 N. Ando, M. Mitsui and A. Nakajima, J. Chem. Phys., 2007,
127, 234305.
19 W. Helfrich and W. G. Schneider, Phys. Rev. Lett., 1965, 14,
229.
20 K. D. Jordan and P. D. Burrow, Chem. Rev., 1987, 87, 557.
21 L. E. Lyons, G. C. Morris and L. J. Warren, J. Phys. Chem.,
1968, 72, 3677.
22 L. Crocker, T. Wang and P. Kebarle, J. Am. Chem. Soc., 1993,
115, 7818.
23 J. Schiedt and R. Weinkauf, Chem. Phys. Lett., 1997, 266,
201.
24 M. Mitsui, N. Ando and A. Nakajima, J. Phys. Chem. A, 2007,
111, 9644.
25 N. Ando, S. Kokubo, M. Mitsui and A. Nakajima, Chem.
Phys. Lett., 2004, 389, 279.
26 M. Tschurl, U. Boesl and S. Gilb, J. Chem. Phys., 2006, 125,
194310.
27 R. S. Becker and E. Chen, J. Chem. Phys., 1966, 45, 2403.
28 L. Wojnárovits and G. Földiák, J. Chromatogr., A, 1981, 206,
511.
29 M. J. Deluca, B. Niu and M. A. Johnson, J. Chem. Phys.,
1988, 88, 5857.
30 T. Tsukuda, M. A. Johnson and T. Nagata, Chem. Phys. Lett.,
1997, 268, 429.
31 A. Bree, F. G. Solven and V. V. B. Vilkos, J. Mol. Spectrosc.,
1972, 44, 298.
32 T. Kato, K. Yoshizawa and K. Hirao, J. Chem. Phys., 2002,
116, 3420.
33 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M.
A. Robb, J. R. Cheeseman, J. J. A. Montgomery, T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
This journal is ß The Royal Society of Chemistry 2013
View Article Online
Published on 19 July 2013. Downloaded by State University of New York at Stony Brook on 30/10/2014 04:31:01.
RSC Advances
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima,
Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H.
P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala,
K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain,
O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J.
This journal is ß The Royal Society of Chemistry 2013
Paper
B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford,
J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M.
W. Wong, C. Gonzalez and J. A. Pople, GAUSSIAN,
Gaussian, Inc., Wallingford CT, 2004.
34 A. Modelli and L. Mussoni, Chem. Phys., 2007, 332, 367.
35 S. Y. Han, J. H. Kim, J. K. Song and S. K. Kim, J. Chem.
Phys., 1998, 109, 9656.
RSC Adv., 2013, 3, 17143–17149 | 17149