228
11 Liquid Phase
Fig. 11.6 NEXFAS spectra of a nanobubbles [98] and b vapor, liquid skin, and bulk liquid [99]. The
spectra resolve discrete peaks that correspond to the bulk, skin, and H–O dangling bond radicals.
Reprinted with permission from [99, 100]
The NEXFAS energy conservation mechanism is different from that of the XPS
[87]. The NEXFAS involves the shift of both the valence band and the O1s core band
but the XPS involves the O 1s band only. The NEXFAS pre–edge shift is the relative
shift of the O1s core level E 1s and its valence band shift E vb (occupied 4a 1 orbital)
from their energy levels of the isolated O atom: E edge = E vb − E 1s ∝ E H > 0
(H–O bond energy) [34]. The E vb is always greater than the E 1s because of the
shielding of electron in the outer electronic orbitals [87].
11.4.4.1 Thermal XAS and DPS: H–O Bond Stability
Figure 11.7 compares the thermal NEXAFS spectra for bulk water and 5M LiCl
solutions. Thermal heating shifts the pre-edge peak for the liquid water negatively
faster than that for the LiCl solutions as the O:H undergoes thermal elongation at
different rates for the deionized water and LiCl solutions [101]. At 25 °C, the cation
effect on the pre-edge shift from the value of 534.67 eV to deeper in alkali chlorides
is remarkable: Li
+ (0.27 eV), Na
+ (0.09 eV), and K
+ (0.00 eV). The energy shift
of Li
+ in the 5 M LiCl solution (0.30 eV) is close to that happened to the 3M
LiCl/H 2 O solution. On the other hand, in the NaCl solution, the anion effect is small:
Cl
− (0.09 eV), Br
− (0.04 eV), and I
− (0.02 eV). The energy trend of the pre-edge shifts
is the same as the differencial phonon spectroscopy (DPS) ω H shifting positively for
the solutions and the skin of water [102].
The contributions from the Li:O polarization or the O:H binding energy are negligibly small. At polarization, the H–O bond becomes shorter and stiffer, the stiffer
H–O bond is thermally more stable than those in the bulk of deionized water, as it
does in the water skin [102].
Figure 11.8 compares the XAS pre-edge thermal shift for the bulk water and the
supersolid hydrating water in the Li
+ hydration shell and the Raman H–O phonon
thermal shift for the concentrated KCl/H 2 O solutions encapsulated in a silica capillary
tube [103]. The XAS peak of the hydration oxygen shifts negatively slower than it
is in the bulk water. The Raman peak 1 at 3200 cm
−1 corresponds to the ω H for
11 Liquid Phase
Fig. 11.6 NEXFAS spectra of a nanobubbles [98] and b vapor, liquid skin, and bulk liquid [99]. The
spectra resolve discrete peaks that correspond to the bulk, skin, and H–O dangling bond radicals.
Reprinted with permission from [99, 100]
The NEXFAS energy conservation mechanism is different from that of the XPS
[87]. The NEXFAS involves the shift of both the valence band and the O1s core band
but the XPS involves the O 1s band only. The NEXFAS pre–edge shift is the relative
shift of the O1s core level E 1s and its valence band shift E vb (occupied 4a 1 orbital)
from their energy levels of the isolated O atom: E edge = E vb − E 1s ∝ E H > 0
(H–O bond energy) [34]. The E vb is always greater than the E 1s because of the
shielding of electron in the outer electronic orbitals [87].
11.4.4.1 Thermal XAS and DPS: H–O Bond Stability
Figure 11.7 compares the thermal NEXAFS spectra for bulk water and 5M LiCl
solutions. Thermal heating shifts the pre-edge peak for the liquid water negatively
faster than that for the LiCl solutions as the O:H undergoes thermal elongation at
different rates for the deionized water and LiCl solutions [101]. At 25 °C, the cation
effect on the pre-edge shift from the value of 534.67 eV to deeper in alkali chlorides
is remarkable: Li
+ (0.27 eV), Na
+ (0.09 eV), and K
+ (0.00 eV). The energy shift
of Li
+ in the 5 M LiCl solution (0.30 eV) is close to that happened to the 3M
LiCl/H 2 O solution. On the other hand, in the NaCl solution, the anion effect is small:
Cl
− (0.09 eV), Br
− (0.04 eV), and I
− (0.02 eV). The energy trend of the pre-edge shifts
is the same as the differencial phonon spectroscopy (DPS) ω H shifting positively for
the solutions and the skin of water [102].
The contributions from the Li:O polarization or the O:H binding energy are negligibly small. At polarization, the H–O bond becomes shorter and stiffer, the stiffer
H–O bond is thermally more stable than those in the bulk of deionized water, as it
does in the water skin [102].
Figure 11.8 compares the XAS pre-edge thermal shift for the bulk water and the
supersolid hydrating water in the Li
+ hydration shell and the Raman H–O phonon
thermal shift for the concentrated KCl/H 2 O solutions encapsulated in a silica capillary
tube [103]. The XAS peak of the hydration oxygen shifts negatively slower than it
is in the bulk water. The Raman peak 1 at 3200 cm
−1 corresponds to the ω H for