bilayer an irreversible increase in the intensities of the methylene stretching modes is
observed (Fig. 3.2b). The positions of the absorption maxima of the ν as (CH 2 ) and
ν s (CH 2 ) modes indicate that the hydrocarbon chains in n-octadecanol bilayers exist
in a solid-like state and adopt a fully stretched all-trans conformation. Therefore, the
values of the θ (νas(CH2)) and θ (νs(CH2)) angles calculated using Eq. (2.47) were
substituted into Eq. (3.1) to determine the tilt of the hydrocarbon chain (θ (chain) ) in
the n-octadecanol bilayer [25, 27].
cos
2
θ νas CH2
ð
Þ
ð
Þ þ cos
2
θ νas CH2
ð
Þ
ð
Þ þ cos
2
θ chain
ð
Þ ¼ 1
ð3:1Þ
In the X-type n-octadecanol bilayer adsorbed directly on the Au(111) surface the
θ (chain) is equal to 18
versus surface normal [25]. At the desorption potential the
θ (chain) increases to 30
. In the re-adsorbed Y-type bilayer the θ (chain) depends on the
electrode potential and varies between 30
and 34
. Zawisza and Lipkowski [25]
used per-deuterated (C 18 D 35 OD) and hydrogenated (C 18 H 35 OH) n-octadecanol to
investigate separately the molecular scale order in each leaflet of the bilayer. The
isotopic substitution ensures ca. 700 cm
À1 bathochromic shift of the ν (CD2) compared
to the ν (CH2) modes (see Sect. 2.3.3). Figure 3.3 shows the θ (chain) versus potential
plots of the tilt of the hydrocarbon chain in the outer electrolyte facing (squares) and
3000 2950 2900 2850
3000 2950 2900 2850
S 0.02
Wavenumber / cm
-1
-0.85
-0.50
-0.30
-0.20
-0.10
0.00
0.20
a)
b)
Fig. 3.2 PM IRRA spectra in the CH stretching modes region of n-octadecanol bilayer on the Au
(111) electrode surface in 0.1 M NaF in (a) first and (b) successive negative going potential scans at
potentials marked in the figure. Electrode potentials are referred versus SCE. Taken from [25] and
modified
50
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .
observed (Fig. 3.2b). The positions of the absorption maxima of the ν as (CH 2 ) and
ν s (CH 2 ) modes indicate that the hydrocarbon chains in n-octadecanol bilayers exist
in a solid-like state and adopt a fully stretched all-trans conformation. Therefore, the
values of the θ (νas(CH2)) and θ (νs(CH2)) angles calculated using Eq. (2.47) were
substituted into Eq. (3.1) to determine the tilt of the hydrocarbon chain (θ (chain) ) in
the n-octadecanol bilayer [25, 27].
cos
2
θ νas CH2
ð
Þ
ð
Þ þ cos
2
θ νas CH2
ð
Þ
ð
Þ þ cos
2
θ chain
ð
Þ ¼ 1
ð3:1Þ
In the X-type n-octadecanol bilayer adsorbed directly on the Au(111) surface the
θ (chain) is equal to 18
versus surface normal [25]. At the desorption potential the
θ (chain) increases to 30
. In the re-adsorbed Y-type bilayer the θ (chain) depends on the
electrode potential and varies between 30
and 34
. Zawisza and Lipkowski [25]
used per-deuterated (C 18 D 35 OD) and hydrogenated (C 18 H 35 OH) n-octadecanol to
investigate separately the molecular scale order in each leaflet of the bilayer. The
isotopic substitution ensures ca. 700 cm
À1 bathochromic shift of the ν (CD2) compared
to the ν (CH2) modes (see Sect. 2.3.3). Figure 3.3 shows the θ (chain) versus potential
plots of the tilt of the hydrocarbon chain in the outer electrolyte facing (squares) and
3000 2950 2900 2850
3000 2950 2900 2850
S 0.02
Wavenumber / cm
-1
-0.85
-0.50
-0.30
-0.20
-0.10
0.00
0.20
a)
b)
Fig. 3.2 PM IRRA spectra in the CH stretching modes region of n-octadecanol bilayer on the Au
(111) electrode surface in 0.1 M NaF in (a) first and (b) successive negative going potential scans at
potentials marked in the figure. Electrode potentials are referred versus SCE. Taken from [25] and
modified
50
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .