ROTATIONAL SPECTROSCOPY OF CO SOLVATED WITH PARA-H 2 MOLECULES Paul Raston and Wolfgang Jäger Department of Chemistry, University of Alberta, Edmonton, AB Canada OSU 2009 S. Baroni and S. Moroni, ChemPhysChem 6, 1884 (2005)

para-H 2 clusters *P. Sindzingre, D. M. Ceperley, M. L. Klein, Phys. Rev. Lett. 67, 1871 (1991) Low temperature (<2 K) para-H 2 clusters are liquid like Small pH 2 clusters predicted to be superfluid below ~2 K.* Rotational temperature of seeded clusters <1 K In this study N pH2 <8

Sample & conditions Typically used % CO % pH 2 in Helium up to 150 bar Nozzle cooled down to -40°C Normal H 2 (75% ortho- + 25% para-) converted to >97% pH 2 in catalytic converter held at <20K for several hours I. F. Silvera, Rev. Mod. Phys. 52, 393 (1980)

FTMW spectrometer Pulsed molecular beam polarized with MW’s: Coherent emission is recorded Good up to ~27 GHz, below which 6 (pH 2 ) N -CO end-over-end transitions should lie

paraH 2 -CO dimer A.V. Potapov, L.A. Surin, V.A. Panfilov, B.S. Dumesh, T.F. Giesen, S. Schlemmer, P.L. Raston and W. Jäger, in preparation. We know transition frequency for N=1 to within ±50 kHz

pH 2 -CO

Previous IR study S. Moroni, M. Botti, S. De Palo, A. R. W. McKellar, J. Chem. Phys. 122, (2005) R 1 (0) line observed for N pH2 <18 Not able to fully separate rotational and vibrational contributions to line position

MW predictions from: Assumption that the vibrational shift scales linearly with N S. Moroni, M. Botti, S. De Palo, A. R. W. McKellar, J. Chem. Phys. 122, (2005)

MW predictions from: Assumption that the vibrational shift scales linearly with N Reptation Monte Carlo simulations S. Moroni, M. Botti, S. De Palo, A. R. W. McKellar, J. Chem. Phys. 122, (2005)

MW lines N=2 found close to IR predicted value

MW lines N=3-6 increasingly further from IR predicted values

MW lines Turnaround of rotational frequency in going from N=6 to 7

Vibrational shift

Switched IR assignment for N=6 & 7

(pH 2 ) N - 13 C 16 O MW lines

(pH 2 ) N - 13 CO MW lines

Summary Assignment (pH 2 ) 2 -CO (pH 2 ) 3 -CO (pH 2 ) 4 -CO (pH 2 ) 5 -CO (pH 2 ) 6 -CO (pH 2 ) 7 -CO pH 2 -He-CO *Tentative

Outlook MW transitions of (pH 2 ) N=2-7 -CO (1216 and 1316) measured and assigned Turnaround in rotational frequency observed in going from N=6 to 7 Extend frequency range of spectrometer and search for N=8 at GHz…. Find 1218 and 1318 lines

Acknowledgements Jäger group Xu group A.R.W. McKellar Funding: University of Alberta Natural Science and Engineering Research Council of Canada Canada Foundation for Innovation Alberta Science and Research Investments Program

PES Reptation Monte Carlo algorithm used to simulate rotational dynamics for N pH2 <18  N =incremental density distribution CO

Assignment Ratio of line intensities for 2 different gas mixtures differing only in the [pH 2 ]; The 2nd mixture contained 0.125x the [pH 2 ] in the 1st Assignments mostly from concentration dependence of line intensities

Comparison with HD solvated HCN D. T. Moore, R. E. Miller, J. Chem. Phys. 119, 4713 (2003)