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
Clusters Microwave Spectroscopy THz Spectroscopy Dimer Microwave Spectroscopy Dyke, T. R., Muenter, J. S., J. Chem. Phys. 1974 2929. 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 1992 257 1937. Liu, K.; Brown, M.G.; Cruzan, J.D.; Saykally, R.J. Science 1996, 271, 62. K. Liu, J. D. Cruzan, R. J. Saykally, Science 1996 271 929. Cruzan, J.D..et al Science 1996, 271 59. Richardson, J. O. et al., J. Phys. Chem. A, 117, 6960 Saykally et al. Science 2016, 352, 1194
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.
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
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
NH3 – (H2O)3 2 1 2 - 1 1 1 S/N = 500:1 kcal/mol NH3 – (water)3 EXP J. Saykally et al., PNAS 2001 98 10533. kcal/mol 2 1 2 - 1 1 1 S/N = 500:1 NH3 – (water)3 EXP RI-MP2/aug-cc-pVDZ A /MHz 3441 3544.17 B /MHz 3192 3324.07 C /MHz 1683 1759.72 V3 / kJ mol-1 5.0 4.3
NH3 – (H2O)4
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 1904.84 C /MHz 977 1001.27 V3 / kJ mol-1 5.5 6.6
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
NH3 – (H2O)5
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 2293.03 B /MHz 1108 1155.69 C /MHz 1051 1087.93 V3 / kJ mol-1 4.4 4.43 4 0 4 - 3 0 3 A E S/N = 70:1
NH3 – (H2O)6 5 0 5 - 4 0 4 S/N = 30:1 NH3 – (water)6 EXP m062x/6-311++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
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 7 0 7 - 6 0 6 S/N = 3:1
AMMNONIA – WATER CLUSTERS (NH3)2 - Water (NH3)2 – (Water)2
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 3189.71 B /MHz 3062 3127.77 C /MHz 1576 1612.75 3 1 3 - 2 1 2 3 0 3 - 2 0 2 Interaction Energy (kcal/mol) Ammonia-Water -6.5 Water-Water -5.0 Ammonia-Ammonia -3.1 S/N = 100:1
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:
Acknowledgements Pate Group NSF MC-IOF 328405 RSC