1. L. Evangelisti,a,c C. Perez,b,c B.H. Patec
International Symposium on Molecular Spectroscopy, 71st Meeting
Champaign-Urbana, June 20-24, 2016
CHARACTERIZATION OF AMMONIA-WATER CLUSTERS BY BROADBAND ROTATIONAL SPECTROSCOPY
L. Evangelisti,a,c C. Perez,b,c B.H. Patec
aDipartimento di Chimica «G. Ciamician», University of Bologna - Italy
bMax-Planck-Institut für Struktur und Dynamik der Materie, Hamburg - Germany
cDepartment of Chemistry, University of Virginia - USA
B. Temelso, G.C. Shields
Dean’s Office, College of Arts and Sciences, and Department of Chemistry, Bucknell University

2. Clusters Microwave Spectroscopy THz Spectroscopy
Dimer
Microwave Spectroscopy
Dyke, T. R., Muenter, J. S., J. Chem. Phys
THz Spectroscopy
Trimer Tetramer Pentamer Hexamer “Cage” Octamer D2d Octamer S4
Liu, K.; Brown, et al. Nature 1996, 381, 501.
N. Pugliano and R. J. Saykally, Science
Liu, K.; Brown, M.G.; Cruzan, J.D.; Saykally, R.J. Science 1996, 271, 62.
K. Liu, J. D. Cruzan, R. J. Saykally, Science
Cruzan, J.D..et al Science 1996,
Richardson, J. O. et al., J. Phys. Chem. A, 117, 6960
Saykally et al. Science 2016, 352, 1194

3. CP-FTMW CP-FTMW Spectroscopy in the 2-18 GHz frequency range.
Optimal results found using a rare gas blown over a reservoir of ammonia hydroxide solution (NH4OH) in a reservoir.
Ne as carrier gas at a total pressure of 6 atm.

4. CP-FTMW 1.2M FID Averages S/N = 25000:1 X 200 X 5000 S/N > 13:1
Frequency / MHz
X 200
X 5000
S/N > 13:1
Frequency / MHz
Frequency / MHz

5. NH3 – (H2O)2 Assigned… 3 transitions! NH3 H2O S/N = 2500:1 X 2 X 2
NH3 – (water)2
EXP
RI-MP2/aug-cc-pVDZ
A /MHz
6971
7093.9
B /MHz
5548
5784.8
C /MHz
3150
3261.6
H2O
S/N = 2500:1
X 2
X 2
1 0 1 – 0 0 0
2 1 2 – 1 1 1
2 0 2 – 1 0 1

6. NH3 – (H2O)3 2 1 2 - 1 1 1 S/N = 500:1 kcal/mol NH3 – (water)3 EXP
J. Saykally et al., PNAS
kcal/mol
S/N = 500:1
NH3 – (water)3
EXP
RI-MP2/aug-cc-pVDZ
A /MHz
3441
B /MHz
3192
C /MHz
1683
V3 / kJ mol-1
5.0
4.3

7. NH3 – (H2O)4

8. NH3 – (H2O)4 4 1 4 - 3 1 3 4 0 4 - 3 0 3 S/N = 60:1 NH3 – (water)4 EXP
RI-MP2/aug-cc-pVDZ
A /MHz
1947
2001.4
B /MHz
1859
C /MHz
977
V3 / kJ mol-1
5.5
6.6

9. NH3 – (H2O)5 Extensively studied ab-initio as a benchmark system.
Structural transition point wherein three-dimensional structures become more stable than the planar ring structures for the smaller clusters.
Several low-energy isomers predicted: Prism, Cage and Book within an energy separation of 1 kJ/mol or less.
RI-MP2/CBS low energy isomers of (H2O)6 sorted in order of increasing electronic energy

10. NH3 – (H2O)5

11. NH3 – (H2O)5 4 0 4 - 3 0 3 A E S/N = 70:1 NH3 – (water)5 EXP
RI-MP2/aug-cc-pVDZ
A /MHz
2121
B /MHz
1108
C /MHz
1051
V3 / kJ mol-1
4.4
4.43 A E
S/N = 70:1

12. NH3 – (H2O)6 5 0 5 - 4 0 4 S/N = 30:1 NH3 – (water)6 EXP
m062x/ g(d,p)
A /MHz
1284
1357.8
B /MHz
928
977.9
C /MHz
901
938.7
V3 / kJ mol-1
4.8
3.59

13. NH3 – (H2O)8 7 0 7 - 6 0 6 S/N = 3:1 NH3 – (water)8 EXP
 RI-MP2/aug-cc-pVDZ
A /MHz
864
885.18
B /MHz
491
493.25
C /MHz
487
479.12
Octamer D2d Octamer S4
S/N = 3:1

14. AMMNONIA – WATER CLUSTERS
(NH3)2 - Water
(NH3)2 – (Water)2

15. Interaction Energy (kcal/mol)
AMMNONIA – WATER CLUSTERS
(NH3)2 – water
theo
A /MHz
6562
B /MHz
5291
C /MHz
3027
Assigned but only 3 transitions…
(NH3)2 – (water)2
EXP
RI-MP2/aug-cc-pVDZ
A /MHz
3120
B /MHz
3062
C /MHz
1576
Interaction Energy (kcal/mol)
Ammonia-Water
-6.5
Water-Water
-5.0
Ammonia-Ammonia
-3.1
S/N = 100:1

16. Ongoing project… Isotopic species such as H218O or 15NH3
Tunneling motions…
Expand the measurement range (at least up to 26 GHz)
Complete the series:
Effect of Deuterium:

17. Acknowledgements
Pate Group
NSF
MC-IOF
RSC