Asymmetry of M+(H2O)RG Complexes, (M=V, Nb) Revealed with
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+ Na+ Asymmetry of M+(H2O)RG Complexes, (M=V, Nb) Revealed with Infrared Spectroscopy Timothy B Ward, Evangelos Miliordos, Sotiris Xantheas, Michael A Duncan Metal-cation water complexes + V (H2O)n 4 1 10 15 20 • Selectivity • Sensitivity 50 100 150 200 250 300 350 400 450 500 550 600 650 700 m/z Mass-Selected Ion Photodissociation Spectroscopy V+(H2O)Ar2 Mass gate on -Ar Fragmentation at 3683 cm-1 0 + hïŪ (IR) ï 50 -Ar 100 150 200 Cation-water interactions • Red shift in the OH stretches • Changes due to polarization removes density along O-H bonds • Free water has ratio of Isym/Iasym 1:18 • Symmetric stretch gains intensity from charge oscillation along symmetry axis Cu+(H2O)Ar2 symmetric stretch, parallel type band 3622 3696 asymmetric stretch, perpendicular type band + Cu (H2O)Ar2 asymmetric stretch-bend combination 3762 3500 3600 3700 cm -1 3800 3900 JPCA 113, 4849 (2009) 3657 3683 + V +(H2O)Ar2 • Many metal ion water complexes have been studied • In most case Ar-M binding energy strong, requiring tagging with multiple Ar atoms 3756 V (H2O)Ar2 3622 3696 + Cu+((H 2 Cu H22O)Ar O)Ar 2 3611 3762 3697 3500 3500 3600 cm 3700 (H23O)Ar3 Co+Co (H2O)Ar 3800 3624 -1 3846 3500 3600 3700 -1 cm 3800 3700 cm + 3400 3600 3900 -1 3800 3900 Sym Asym ðđ ð―, ðū = ðĩð― ð― + 1 + ðī − ðĩ ðū 2 • A special situation happen if: • Tagging with one Ar • Ar is on C2 axis with metal-water para K’ = 2 v=1 • Treat as prolate symmetric trop ortho 4A’ K’ = 1 K‘ = 0 1x 3x K“ = 1 v=0 JCP 134, 014302 (2011) 2A’’ K“ = 0 Cation Binding Increase H-O-H Angle Ca+ + Mg • Using A” we can calculate the HOH bond angle, if we assume that the OH bond length is constant O • This has been done for several cation-water complexes o o 2.22 A 2.03 A O H H O H H 104.5o 106.8o 110.6o JPCA 109, 7057 (2005) JCP 104, 4591 (1996) Cr+ Li+ O O H H 106.3o H H H PCCP 8, 3078 (2006) 111.9o H JPCA 112, 6237 (2008) Nb+(H2O)Ar is different! Nb+(H2O)Ar • Still seem to have two OH stretch bands, that are red shifted • Asymmetric stretch still looks to have rotational structure, but different pattern PGOPHER Simulation 3500 Duncan and co-workers, J. Chem. Phys., 2011, 134, 3550 3600 3650 cm -1 3700 3750 3800 • Ne tagging shows that we only have two OH stretches Vanadium-water also has unusual pattern • Same rotational intensity issue arises in V+(H2O)Ar 3604 V+(H2O)Ar 3673 3589 3673 3589 3705 3694 3667 3692 3674 3684 3630 3650 Nb+(H2O)Ar Nb+(H2O)Ne 3665 3500 3500 3550 3600 3650 cm -1 3700 3750 3800 3550 3600 3650 cm -1 3700 3750 3800 Theory by E. Miliordos and S.S. Xantheas at Pacific Northwest National Lab Nb+(H2O) • icMRCI and CCSD(T) methods • aug-cc-pVQZ for H, O, and Ar • cc-pVQZ for V • cc-pVQZ-PP for Nb • Calculations show C2v for the metal-water • Argon however is off axis v=2 v=1 v=0 • V also has out of plane Ar V+(H2O) • This explains smaller spacing but not intensities v=2 v=1 v=0 PGOPHER Simulation 3500 3550 3600 3650 cm -1 3700 3750 3800 Need an effect to change line intensities How to probe ortho-para mixing? Isotropic Fermi Contact from Xantheas and Miliordos • Isotopic Fermi Contact • Here it defines interaction of 1H nuclear spin with clusters total electronic spin • ak, bk, and ck are the three eigenvalues of the spin-dipole tensor • ðŧ hf = • The hamiltonian for the interaction between two magnetic moments (nuclear and electronic) • Nb and V much greater than Sc K ðīK ð â ðžK +ð ðð ðžK Normal 3:1 ortho-para ratio Constant M = Sc (3Α1) (MHz) M = V (5B1) (MHz) M = Nb (5B1) (MHz) AK 0.42 2.17 3.46 ak -4.28 -13.01 -11.76 bk -3.88 -12.98 -10.12 ck 8.16 25.99 21.87 Nb+(H2O)Ar A” = 11.5 cm-1 B”/C”= 0.0476 cm-1 A’ = 10.5 cm-1 B’/C’= 0.0476 cm-1 T = 40 K Ortho-Para mixed PGOPHER Simulation B.O.sym = 3589 cm-1 B.O.asym = 3662 cm-1 Ortho-Para 3:1 PGOPHER Simulation 3500 3550 3600 3650 cm -1 3700 3750 3800 V+(H2O)Ar A” = 5.5 cm-1 B”/C”= 0.0542 cm-1 A’ = 10.5 cm-1 B’/C’= 0.0542cm-1 T = 40 K Ortho-Para mixed PGOPHER Simulation B.O.sym = 3604 cm-1 B.O.asym = 3690 cm-1 Ortho-Para 3:1 PGOPHER Simulation 3500 3550 3600 3650 cm -1 3700 3750 3800 Conclusions • Ar seems to be out of C2v 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 106 s-1 • This compares well reasonably with Tanaka and co-workers 1.2*105 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
