Delayed Ionization of UO 2 and PFIZEKE spectroscopy

Delayed Ionization of UO 2 and PFI-ZEKE spectroscopy of UO 2+ Jeremy Merritt, Jiande Han, and Michael Heaven Department of Chemistry Emory University Atlanta, GA 30322 62 nd OSU International Symposium on Molecular Spectroscopy June 18 -22, 2007 Do. E

Understanding Actinides is Important … Nuclear energy Push our understanding of chemical bonding Role of f electrons on chemical bond formation Relativistic effects Calculations are difficult; but environmentally friendly Need to benchmark theory; Gas phase data is ideal Multiple Oxidation States Cations are especially prevalent in solution

Experimental Apparatus MCP 1 UOx+ Depleted 238 U rod hv 2 Skimmer Einzel lens 0. 1% O 2 in He Pulsed valve UOx+He Grids e- Vaporization Laser 532 nm, 10 m. J hn 1 MCP 2

Previous results on UO 2 J. Han et al. J. Chem. Phys. , 120, 5155 (2004) UO 2++en 2 (fixed) UO 2+ signal 2 g IP = 6. 128(3) e. V n 1 3 u X 3 F 2 nd color energy (cm-1) 2 u REMPI Previously accepted IP = 5. 4(1) e. V

Delayed ionization of UO 2 Ionization high above threshold UO U UO 2 Ionization just at threshold

Delayed ionization of UO 2 Ground state of UO 2+ is embedded in A manifold of excited states of the neutral UO+ + O UO + O IP r n 2 D 0

PFI-ZEKE of UO 2 hv 2 -6. 8 V (1. 29 V cm-1) -5 V e 0 Pulsed Field Ionization MCP 2 2 Photon excitation hn 1 4 hv 2 hv 1 t/ms ZEKE Energy Balance: hn 1 + hn 2 = IP + Eion(Te, V, J) + Eke 0

I. P. Refinement for UO 2 Eion(v, J) hv 2 2 g hv 1 (fixed) X 3 F 2 u ZEKE DE = 5 cm-1 I. P. = 6. 127(1) e. V

UO 2+ ZEKE Spectra Eion(v, J) IP hv 2 2 g 920 cm-1 hv 1 (fixed) X 3 F 2 u 145 cm-1 ZEKE 145 cm-1

Scanning ……….

nss = 0 Ev = (v+1/2)hwe – (v+1/2)2 hwexe

nss = 0 nss = 1 Ev = (v+1/2)hwe – (v+1/2)2 hwexe

nss = 0 nss = 1 nss = 2 Ev = (v+1/2)hwe – (v+1/2)2 hwexe

nss = 0 nss = 1 nss = 2 nss = 3 Ev = (v+1/2)hwe – (v+1/2)2 hwexe

nss = 0 nss = 1 nss = 2 nss = 3 nss = 4 Ev = (v+1/2)hwe – (v+1/2)2 hwexe

Excited Electronic state Ev = (v+1/2)hwe – (v+1/2)2 hwexe

Ground Electronic State nss = 0 we = 145. 5 wexe = 0. 30 nss = 1 we = 143. 2 wexe = 0. 14 918. 5 924. 5 nss = 2 we = 141. 6 wexe = 0. 18 nss = 3 we = 136. 2 wexe = 0. 15 nss = 4 we = 135. 8 wexe = 0* 913. 5 915. 5 1 st excited Electronic State nss = 0 we = 135. 3 wexe = 0* 926. 6 nss = 1 we = 138. 3 wexe = 0* 2677. 9 +0 -nbend

238 U 18 O 2 Ground Electronic State nss = 0 we = 145. 5 137. 9 wexe = 0. 30 0. 25 nss = 1 we = 143. 2 137. 8 wexe = 0. 14 0. 24 we = 141. 6 138. 6 wexe = 0. 18 0. 22 nss = 3 we = 136. 2 wexe = 0. 15 nss = 4 we = 135. 8 wexe = 0* nss = 2 918. 5 860. 3 924. 5 860. 1 913. 5 915. 5 Exp 1 st excited Electronic State nss = 0 nss = 1 we = 135. 3 133. 1 we = 138. 3 wexe = 0* 0. 51 wexe = 0* 2677. 9 +0 -nbend 2671. 3 0. 948 926. 6 0. 937 Theory

Where do we expect the electronic states? U: 5 f 3 6 d 1 7 s 2 UO 2 = O 2 - U 4+(5 f 2) O 2 - 2 F 7/2 7609 cm-1 UO 2+ = O 2 - U 5+(5 f) O 2 - 6567 5751 2736 2 F 2 F 5/2 0 cm-1 2677. 9 +0 -nbend 0 W: 7/2 5/2 3/2 1/2 U 5+ O 2 - I. Infante et al. Dirac-Coulomb intermediate Hamiltonian MRCC approach [DC-IHFSCC] 40 e-, 5 f, 6 d, 7 s active space; 4 component SOC included Jean BLAISE and Jean-François WYART, Selected Constants Energy Levels and Atomic Spectra of Actinides.

More Comparisons with Theory 918. 5 cm-1 DFT [B 3 LYP] 145. 5 cm-1 r. UO = 1. 764 Å 936(sg), 148 (pu), 1010 (su) Andrews et. al. J. Phys. Chem. A 2000, 104, 5495 -5502 (12/12) Bigger basis

Summary and Conclusions • PFI-ZEKE spectroscopy for polyatomic actinide cations • Accurate IP Measurements • Bending, SS, and 1 st electronic state Energies accurately determined • Frank-Condon? ? ?