Supplementary Material
Structure and Intermolecular Dynamics of an Equimolar Benzene and 1,3
Dimethylimidazolium Bis[(trifluoromethane)sulfonyl]amide Mixture:
Molecular Dynamics Simulations and OKE Spectroscopic Measurements
Ruth M. Lynden-Bell*
Department of Chemistry
Cambridge University
Cambridge CB2 1EW, England
Lianjie Xue, George Tamas, and Edward L. Quitevis*
Department of Chemistry & Biochemistry
Texas Tech University
Lubbock, TX 79409
Corresponding authors: rmlb@cam.ac.uk and edward.quitevis@ttu.edu
Table S1. Multicomponent Line Shape Analysis Fit Parametersa,
Benzene
[dmim][NTf2]
Benzene/[dmim][NTf2]
Ideal mixture
ABL
0.27413
0.04647
0.10147
0.10034
a
1.3505
1.1898
1.1844
1.3447
BL/cm-1
9.6568
13.303
11.019
9.6463
AG1
4.3192
0.36045
0.50251
0.52617
G1/cm-1
51.285
60.945
29.035
17.88
1/cm-1
41.93
25.876
54.226
36.61
AG2
0.11558
0.29291
0.94796
1.2598
G2/cm-1
161
101.68
64.001
63.658
2/cm-1
19.904
23.495
39.288
41.846
AG3
0.11782
0.04613
0.026137
0.03211
G3/cm-1
207.24
122.41
121.82
124.97
3/cm-1
33.894
5.6476
11.03
6.2892
AG4
0.07611
0.0494
0.00551
G4/cm-1
134.82
124.93
191.49
4/cm-1
14.613
11.805
9.5591
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Supplementary Material
0.08943
0.10929
0.08328
G5/cm-1
166.41
166.5
167.58
5/cm
13.851
18.537
17.999
0.10949
0.08648
0.10459
202.49
202.37
204.07
AG5
-1
AG6
G6/cm
-1
6/cm-1
AG7
19.017
15.912
0.04897
0.06013
249.97
241.83
G7/cm-1
-1
17.778
29.335
7/cm
a
See eq 2 and 3 in paper for definition of fit parameters.
18.752
0.04985
246.7
17.006
[NTf2]- Density of States
In Figure S1 we show the density of states for the [NTf2]- anion in neat [dmim][NTf2] in the
1:1 benzene/[dmim][NTf2] mixture. The peaks are due to intramolecular modes, which are
insensitive to the surroundings. Note that the frequencies of the intramolecular modes in the
simulation are lower than those in the experimental RSDs. The difficulty with the anion density
of states is that the force fields used in MD simulations are fitted to thermodynamic and dynamic
properties such as density and self-diffusion coefficients. The emphasis and interest in the
current paper is on the intermolecular interactions. Usually the torsional parameters are also
fitted to quantum chemical calculations, but the other vibrational modes are not really
considered. Thus we would not really expect good agreement with the Raman or IR spectra. The
torsional fit for [NTf2]- is shown by Koeddermann et al.1,2 There is a further complication, in that
united CF3 groups are used in this calculation as was done by Koeddermann et al. The mass of
the united CF3 atom is 69. This will mean that the vibrations involving for example S-(CF3) and
N-S-(CF3) will be much lower in frequency than the corresponding S-C or N-S-C would be. This
is probably the main reason that the internal vibrations appear at such a low frequency in the
model.
2
Supplementary Material
Figure S1. Density of states for the [NTf2]-anion in the mixture and in
neat [dmim][NTf2]. The peaks are due to internal modes which are
insensitive to the surroundings.
Benzene Density of States
Figure S2 shows that in neat benzene, the translational DOS spans the same frequency range
as the total DOS, with both peaked at ~13 cm-1. However, relative to the peak there is less in
intensity in the tail region for the translational DOS than the total DOS. Thus if translational
modes contribute to the RSD, suppressing the translational modes should have a greater effect on
the low frequency side of the RSD than on the high frequency side. However, based on their
OKE spectroscopic study on isotopologues of benzene, Fourkas and workers3 have argued that
hindered rotational motions largely underlies the RSD of benzene. Therefore, if one accepts this
interpretation of the RSD of benzene, suppression of the translational modes cannot be the
reason for deviation of the experimental mixture RSD from the ideal mixture RSD for the
benzene/[dmim][NTf2] mixture.
3
Supplementary Material
Figure S2. Density of states for benzene in the neat liquid.
References
1
T. Koddermann, D. Paschek, and R. Ludwig, ChemPhysChem 8, 2464 (2007).
2
T. Koddermann, D. Reith, and R. Ludwig, ChemPhysChem 14, 3368 (2013).
3
K. Manfred, X.-X. He, and J. T. Fourkas, J. Phys. Chem. B 114, 12096 (2010).
4