24.3 DPS of Water and Solutions
479
the pump-probe ultrafast IR spectroscopy, the phonon population decay, or vibration
energy dissipation, rate is proportional to the phonon frequency—the dynamics of
higher frequency phonon is associated with a faster process.
Figure 24.5 compares the segmental ω x DPS for the concentrated HX/H 2 O solutions [7] and for the heated water [36]. The ω L and the ω H relax indeed cooperatively
for all acidic solutions and the heated water. As the concentration increases from 0
to 0.1, X − polarization transits the ω L from 180 to 75 cm
−1 and the ω H from 3200 to
3480 cm
−1 [37]. H↔H repulsion reverts the ω L from 75 cm
−1 to 110 cm
−1 . The DPS
also resolves the effect of the H↔H repulsion on the H–O bond elongation featured
as a small hump below 3050 cm
−1 . The H↔H repulsion lengthens its neighboring
H–O bonds, as being the case of mechanical compression and O:⇔:O point compression in basic solutions [22]. The fraction of H–O bonds elongation by H↔H
repulsion decreases when the X − turns from Cl − to Br − and I − as the stronger polarizability of I − annihilates the effect of H↔H repulsion. The small spectral valley at
3650 cm
−1 results from the preferential skin occupation of X − that strengthens the
ΔI(a.u.)
ω H (cm
-1
)
0.02
0.04
0.06
0.08
0.10
(a)
(b)
HCl/H 2 O
X
- polarization
H-H repulsion
2800
3000
3200
3400
3600
50
100
150
200
250
300
0.02
0.04
0.06
0.08
0.10
H−H
repulsion
ΔI(a.u.)
ω L (cm
-1 )
HCl/H 2 O
2800
3000
3200
3400
3600
Δ I(a.u.)
ω H (cm
-1
)
(c)
358 K
298 K
H-O thermal
contraction
H 2 O
50
100
150
200
250
300
298 K
ΔI (a.u.)
ω L (cm
-1
)
(d)
H 2 O
358 K
O:H thermal
elongation
Fig. 24.5 DPS ω x for the a, b concentrated HCl/H 2 O solutions [7], and the c, d heated water
[10]. The blueshift in a arises from X − polarization and the humps below 3100 cm −1 from H↔H
repulsion. The joint effect of polarization and repulsion shifts the ω L in b to 110 cm −1 . H–O thermal
contraction shifts ω H from 3200 to 3500 cm −1 and the O:H elongation shifts the ω L from 200 to
75 cm −1 . Reprinted with permission from [7]
479
the pump-probe ultrafast IR spectroscopy, the phonon population decay, or vibration
energy dissipation, rate is proportional to the phonon frequency—the dynamics of
higher frequency phonon is associated with a faster process.
Figure 24.5 compares the segmental ω x DPS for the concentrated HX/H 2 O solutions [7] and for the heated water [36]. The ω L and the ω H relax indeed cooperatively
for all acidic solutions and the heated water. As the concentration increases from 0
to 0.1, X − polarization transits the ω L from 180 to 75 cm
−1 and the ω H from 3200 to
3480 cm
−1 [37]. H↔H repulsion reverts the ω L from 75 cm
−1 to 110 cm
−1 . The DPS
also resolves the effect of the H↔H repulsion on the H–O bond elongation featured
as a small hump below 3050 cm
−1 . The H↔H repulsion lengthens its neighboring
H–O bonds, as being the case of mechanical compression and O:⇔:O point compression in basic solutions [22]. The fraction of H–O bonds elongation by H↔H
repulsion decreases when the X − turns from Cl − to Br − and I − as the stronger polarizability of I − annihilates the effect of H↔H repulsion. The small spectral valley at
3650 cm
−1 results from the preferential skin occupation of X − that strengthens the
ΔI(a.u.)
ω H (cm
-1
)
0.02
0.04
0.06
0.08
0.10
(a)
(b)
HCl/H 2 O
X
- polarization
H-H repulsion
2800
3000
3200
3400
3600
50
100
150
200
250
300
0.02
0.04
0.06
0.08
0.10
H−H
repulsion
ΔI(a.u.)
ω L (cm
-1 )
HCl/H 2 O
2800
3000
3200
3400
3600
Δ I(a.u.)
ω H (cm
-1
)
(c)
358 K
298 K
H-O thermal
contraction
H 2 O
50
100
150
200
250
300
298 K
ΔI (a.u.)
ω L (cm
-1
)
(d)
H 2 O
358 K
O:H thermal
elongation
Fig. 24.5 DPS ω x for the a, b concentrated HCl/H 2 O solutions [7], and the c, d heated water
[10]. The blueshift in a arises from X − polarization and the humps below 3100 cm −1 from H↔H
repulsion. The joint effect of polarization and repulsion shifts the ω L in b to 110 cm −1 . H–O thermal
contraction shifts ω H from 3200 to 3500 cm −1 and the O:H elongation shifts the ω L from 200 to
75 cm −1 . Reprinted with permission from [7]