Cristobal Perez Matt T Muckle Daniel P Zaleski Nathan Seifert Brooks H Pate Department of Chemistry University of Virginia Charlottesville Virginia USA Z bigniew Kisiel Institute of Physics Polish Academy of Sciences ID: 630463
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Slide1
Water clusters observed by chirped-pulse rotational spectroscopy: Structures and hydrogen bonding
Cristobal Perez, Matt T. Muckle, Daniel P. Zaleski, Nathan Seifert, Brooks H. PateDepartment of Chemistry, University of Virginia, Charlottesville, Virginia, USAZbigniew KisielInstitute of Physics, Polish Academy of Sciences,Warszawa, PolandBerhane Temelso, George C. ShieldsBucknell University, Lewisburg, Pennsylvania, USA
6
7th OSU International Symposium on Molecular Spectroscopy RH03Slide2
Comparison of chirped pulse and Balle-Flygare type spectra:
Transitions for the cage water hexamer (frequencies/MHz)Chirped pulse spectrum = 8 GHz width recorded overnight Balle-Flygare spectrum = 1 MHz width recorded in 10 minutes
IFPAN
BF, cavityVIRGINIAchirpedSlide3
Hexamer structure determination I: Kraitchman equations
Substitution oxygen atom coordinates (Å) :Slide4
Hexamer structure determination II: least squares
r0 geometryOxygen framework geometry requires determination of 3N-6=12 internal structural parameters21 experimental moments of inertia are available (parent+six
18O species)
Fit made with the STRFIT program from PROSPE website
B
obs
-
B
calc
< 0.31 MHzSlide5
Evolution of assumptions concerning the indeterminable structural parameters of the hydrogens:
Assessed by the value of the total deviation of the least squares fit (in uÅ
2
units) Slide6
Comparison of experiment (dark red) and
calculation (semi-transparent):Experiment = r0
Experiment = r
sCalculation = vibrationally averaged MP2/aug-cc-pVDZ
Try out the rotatable 3D models in Fig.3 of Perez et al.,
Science
336
, 897 (2012)Slide7
expt.,
r0 calc., vibrationally
averaged MP2/aug-cc-pVDZ
9 hydrogen bonds all 6 H2O’s with 3 H-bonds
E
=
+ 0.0 kJ/mol
?!
Water detachment energy (kJ/mol)Slide8
8
hydrogen bonds 2 H2O’s with 2 H-bonds4 H2O’s with 3 H-bonds
uu{1}
E = + 0.9 kJ/mol ?!Slide9
7
hydrogen bonds4 H2O’s with 2 H-bonds2 H2O’s with 3 H-bonds
E = + 2.7 kJ/molSlide10
The smallest water clusters and O...O distances:
2.98 Å2.84 Å2.80 Å
2.76 Å
Saykally + Wales, Science 336, 814 (2012)Slide11
O...O distances in clusters and bulk water:
Liu, Brown, Cruzan, Saykally, J.Phys.Chem. A 101, 9011 (1997)?Slide12
A.K.Soper,
Chem.Phys. 258,121 (2000)neutron diffraction revised to 2.8 ÅHexamer O...O distances and the radial distribution function for liquid water:
Book: 2.886 Å
Prism: 2.802 Å
Cage: 2.852 Å
Cage + Prism +
Book,
r
0
distances
Uwe Bergmann
et al.
JCP
127
,174504 (2007)
X-ray Raman:
liquid = 2.81 Å
ice Ih = 2.76 Å
Long standing OO distance in liquid water = 2.84 Å
(neutron diffraction)Slide13
There is remarkable agreement between experiment and computation concerning the variation in O
...O bond distances ... allowing more confident, detailed insight into the hydrogen bonding network for each isomer. Slide14
The O
...O distance is a known measure of hydrogen bond strength and in the hexamer isomers these span the range 2.70 to 3.01 Å. This is a departure from the more uniform picture for (global minimum)
clusters up to the water
pentamer in which symmetry enforces a single O...O distance, systematically decreasing with cluster size. The
shortest O
...
O distance in the
hexamers
is shorter than
2.76
Å
in
the
pentamer
, whereas the longest
hexamer
O
...
O distance exceeds
2.98
Å
for
the water
dimer
.
Slide15
The water
detachment energies show large variation but correlate with the O...O distances and with the number of hydrogen bonds to each water monomer. Slide16
The water heptamer, (H
2O)7:All seven single 18O species assigned rs analysis without imaginary coordinates (unlike in the hexamers)Least squares r
0 fit possible but rm
(1) geometry is even better: very low deviation of fit of 0.0069 uA2The rm(1) geometry probably accounts for hydrogen indeterminacies and compares well with
ab initio
equilibrium
Average nearest
neighbour
OO distances:
r
0
= 2.8
48
Å
liquid = 2.81
Å
r
s
= 2.8
35
Å
r
m
(1)
= 2.8
23
Å
r
m
(1)
compared with equilibrium
ab
initioSlide17
Similarity between the (H
2O)7 and the prism (H2O)6 structures:
r
0
compared with
vibrationally
averaged
ab
initio
E
disp
E
es
All other H-bonds:
E
disp
E
es
/2Slide18
This
(work) provides a consistent picture of the diversity of hydrogen bonding appearing at the hexamer cluster level ...... which is a small scale prelude to the known diversity in the structure of liquid water. C.Perez et al.,
et al., Science 336
, 897 (2012)