Asymmetry of M + (H 2 O)RG Complexes, (M=V, Nb) Revealed with Infrared Spectroscopy Timothy B Ward, Evangelos Miliordos, Sotiris Xantheas, Michael A Duncan + Na +

Selectivity Sensitivity Metal-cation water complexes

+ h (IR)  Mass gate on V + (H 2 O)Ar 2 -Ar Fragmentation at 3683 cm -1 Mass-Selected Ion Photodissociation Spectroscopy

JPCA 113, 4849 (2009) Cation-water interactions Cu + (H 2 O)Ar 2 asymmetric stretch, perpendicular type band symmetric stretch, parallel type band asymmetric stretch-bend combination Red shift in the OH stretches Changes due to polarization removes density along O-H bonds Free water has ratio of I sym /I asym 1:18 Symmetric stretch gains intensity from charge oscillation along symmetry axis

V + (H 2 O)Ar 2 Co + (H 2 O)Ar 3 Cu + (H 2 O)Ar 2 Many metal ion water complexes have been studied In most case Ar-M binding energy strong, requiring tagging with multiple Ar atoms

A special situation happen if: Tagging with one Ar Ar is on C 2 axis with metal-water Treat as prolate symmetric trop Sym Asym JCP 134, (2011)

Using A” we can calculate the HOH bond angle, if we assume that the OH bond length is constant This has been done for several cation-water complexes Cation Binding Increase H-O-H Angle JPCA 112, 6237 (2008) PCCP 8, 3078 (2006) JPCA 109, 7057 (2005) JCP 104, 4591 (1996)

Still seem to have two OH stretch bands, that are red shifted Asymmetric stretch still looks to have rotational structure, but different pattern Nb + (H 2 O)Ar Duncan and co-workers, J. Chem. Phys., 2011, 134, Nb + (H 2 O)Ar is different!

Ne tagging shows that we only have two OH stretches Same rotational intensity issue arises in V + (H 2 O)Ar Nb + (H 2 O)Ar Nb + (H 2 O)Ne V + (H 2 O)Ar Vanadium-water also has unusual pattern

Theory by E. Miliordos and S.S. Xantheas at Pacific Northwest National Lab icMRCI and CCSD(T) methods aug-cc-pVQZ for H, O, and Ar cc-pVQZ for V cc-pVQZ-PP for Nb Calculations show C 2v for the metal-water Argon however is off axis v = 0 v = 1 v = 2 Nb + (H 2 O)

V also has out of plane Ar This explains smaller spacing but not intensities v = 0 v = 1 v = 2 PGOPHER Simulation V + (H 2 O)

Need an effect to change line intensities

ConstantM = Sc ( 3 Α 1 ) (MHz) M = V ( 5 B 1 ) (MHz) M = Nb ( 5 B 1 ) (MHz) AKAK akak bkbk ckck How to probe ortho-para mixing? Isotropic Fermi Contact from Xantheas and Miliordos Normal 3:1 ortho-para ratio

Nb + (H 2 O)Ar A” = 11.5 cm -1 B”/C”= cm -1 A’ = 10.5 cm -1 B’/C’= cm -1 T = 40 K B.O. sym = 3589 cm -1 B.O. asym = 3662 cm -1 Ortho-Para mixed Ortho-Para 3:1

V + (H 2 O)Ar A” = 5.5 cm -1 B”/C”= cm -1 A’ = 10.5 cm -1 B’/C’= cm -1 T = 40 K B.O. sym = 3604 cm -1 B.O. asym = 3690 cm -1 Ortho-Para mixed Ortho-Para 3:1

Conclusions Ar seems to be out of C 2v plane, lowering the value of A” and A’ for both Nb and V Nb and V are examples where nuclear spin is catalyzing ortho-para interconversion Rate is approximately 10 6 s -1 This compares well reasonably with Tanaka and co-workers 1.2*10 5 s -1 torr -1 for open-shelled vinyl radical

Acknowledgements Michael Duncan The Duncan lab Sotiris Xantheas Evangelos Miliordos Gary Douberly Department of Energy University of Georgia