Washington State University Pacific Northwest National Laboratory Photoelectron Spectroscopy of Multiply-Charged Anions Lai-Sheng Wang Department of Physics, Washington State University & Chemical & Materials Sciences Division, Pacific Northwest National Laboratory Anion /29 – 7/3, 2007 Park City, Utah Ken: Congrat to your (60±1)th B-Day!

Washington State University Pacific Northwest National Laboratory Multiply-charged anions were rarely observed in the gas phase

Washington State University Pacific Northwest National Laboratory J. Chem. Phys. 50, 1896 (1969) The earliest observed doubly charged anion

Washington State University Pacific Northwest National Laboratory Phys. Rev. Lett. 67, 1242 (1991) Doubly-charged carbon clusters and fullerenes C n 2– (n = 7-28) by Cs + sputtering of graphite Phys. Rev. Lett. 65, 625 (1990) J. Am. Chem. Soc. 113, 6795 (1991)

Washington State University Pacific Northwest National Laboratory Experimental: Mass spectrometry observations (70’) Compton et al.: first observation of C n 2- (n = 7-28) (1990) C : Coe et al. and Compton et al. (91’) Kebarle, Lau, etc: electrospray (mid-90’s) Theoretical: (1990’s) Boldyrev/Gutsev (J. Phys. Chem. 94, 2256, 1990) high EA species; M k X k+1 - or (MX) k X -, stable dianions M k X k+2 2- Cederbaum (Scheller, Compton & Cederbaum, Science 270, 1160, 1995) Simons/Boldyrev/Gutowski (Acc. Chem. Res. 29, 497, 1996) Ortiz Landman … Prior research on multiply-charged anions

Washington State University Pacific Northwest National Laboratory Multiply-charged anions are common in the condensed phase Simple oxo-anions SO 4 2-, CO 3 2-, PO 4 3-, C 2 O 4 2-, S 2 O 8 2-, Si 2 O 5 2-, CrO 4 2-, Cr 2 O 7 2-, VO 4 3-, RuO 4 3- … Inorganic and organometallic multiply- charged anions MX 4 2-, MX 6 2-, (X = Metal, X = halides)… Organic multiply-charged anions Biomolecules

Washington State University Pacific Northwest National Laboratory Electrospray Ionization Interface between solution and gas phase John B. Fenn et al. J. Phys. Chem. 88, 4451 & 4671 (1984): Nobel Prize HV Electrospray Capillary Heated Desolvation Capillary Skimmer M n- M beam EvaporationBreakup Charged droplets Kebarle, Lau, etc: ESI MS of MCA (mid-90’s)

Washington State University Pacific Northwest National Laboratory

Washington State University Pacific Northwest National Laboratory

Washington State University Pacific Northwest National Laboratory Solution-phase chemistry in the gas phase Unique properties of multiply-charged anions Electronic structure of solution anions and complexes in the gas phase Solvation and solvent stabilization of complex and multiply-charged anions Probing the electronic structure of Fe-S clusters, complexes and Fe-S proteins Re 2 Cl 8 2-, S 2 O 8 2-, Cr 2 O 7 2-, H 2 P 2 O 7 2-, Ru 6 (CO) 18 2-, ZrF 6 2-, ML 6 2- (M = Re, Os, Ir, Pt), … J. Chem. Phys. 111, 4497 (1999); 112, 6959 (2000); J. Am. Chem. Soc. 112, 2096 (2000); 112, 2339 (2000); J. Phys. Chem. A 104, 4429 (2000); 105, (2001); J. Am. Chem. Soc. 122, 8305 (2000)… SO 4 2- (H 2 O) n, C 2 O 4 2- (H 2 O) n, NO 3 - (H 2 O) n, F - (H 2 O) n, - O 2 C-(CH 2 ) x -CO 2 - (H 2 O) n, … Science 294, 1322 (2001); J. Chem. Phys. 113, (2001); 115, 2889 (2001); 116, 561 (2002); J. Phys. Chem. A 106, 7607 (2002); J. Am. Chem. Soc. 124, (2002); JACS 126, xxx (2004)… Phys. Rev. Lett. 89, (2002); J. Phys. Chem. A 107, 1703 (2003); 107, 2821 (2003); 107, 2898 (2003); J. Phys. Chem. A 107, 4612 (2003); J. Am. Chem. Soc. 125, (2003)… Nature 400, 245 (1999); Phys. Rev. Lett. 81, 2667 (1998); 81, 3351 (1998); J. Chem. Phys. 110, 3635 (1999); Phys. Rev. Lett. 83, 3402 (1999); J. Phys. Chem. A 104, 1978 (2000); Chem. Phys. Lett. 307, 391 (1999);…

Washington State University Pacific Northwest National Laboratory Current experimental effort on multiply charged anions Compton: Coulomb barrier, electron attachment (ESI) Kappes: PES, laser detachment, lifetime in a Penning trap ESI/Laser ablation Denmark group (Nielsen, Andersen, Hvelplund): electron scattering, charge transfer in storage ring (ESI) Mainz group (Herlert, Schweikhard): Multiply charged anion formation in a Penning trap Neumark/Woste/Meijer: IR of SO42-(H2O)n- Wiliams: MS and IR of SO42-(H2O)n- Dessent …… ESI is gaining popularity as a powerful ion source not just for analytical mass spectrometry, but also for physical chemistry and spectroscopy

Washington State University Pacific Northwest National Laboratory Photoelectron spectroscopy of singly and multiply-charged anions

Washington State University Pacific Northwest National Laboratory Difference between photodetachment of singly and multiply-charged anions

Washington State University Pacific Northwest National Laboratory Repulsive coulomb barrier (RCB) and negative electron binding energies

Washington State University Pacific Northwest National Laboratory The first PES of a doubly charged anion: Direct observation of the RCB Wang, Ding & Wang, Phys. Rev. Lett. 81, 3351 (1998) Citrate 355 nm 266 nm

Washington State University Pacific Northwest National Laboratory 266 nm355 nm Intramolecular coulomb repulsion and RCB Wang, Ding, Wang & Nicholas, Phys. Rev. Lett. 81, 2667 (1998)

Washington State University Pacific Northwest National Laboratory Wang, Ding, Wang & Nicholas Phys. Rev. Lett. 81, 2667 (1998) EB + RCB = constant = 3.2 eV ! = electron binding energy of R-CO 2 – Intramolecular coulomb repulsion and RCB C—–(CH 2 ) n —–C O O O O ΘΘ rnrn r RCB = e 2 /r = 14.4/r (eV.Å)

Washington State University Pacific Northwest National Laboratory Observation of negative electron binding energies: photoelectron spectra of [CuPc(SO 3 ) 4 ] 4- and [CuPc(SO 3 ) 4 H] 3- X. B. Wang & L. S. Wang, Nature 400, 245 (1999) Kappes et al., isomer-dependent life times: J. Phys. Chen. A 107, 794 (2003)

Washington State University Pacific Northwest National Laboratory Isolated SO 4 2- and PO 4 3- Anions Do Not Exist –Boldyrev & Simons, J. Phys. Chem. 98, 2298 (1994) –SO > SO e -, -1.6 eV Blades & Kebarle, J. Am. Chem. Soc. 116, (1994) –ESI of Na 2 SO 4 solution –Observed SO 4 2- (H 2 O) n, n = 4-16 Questions: –Minimum number of H 2 O needed to stabilize SO 4 2- –How is SO 4 2- solvated? –Inside or outside? –Solvation shell? Solvation and solvent stabilization of multiply-charged anions

Washington State University Pacific Northwest National Laboratory ESI Mass Spectra of SO 4 2- (H 2 O) n Blades & Kebarle J. Am. Chem. Soc. 116, (1994)

Washington State University Pacific Northwest National Laboratory PES of SO 4 2– (H 2 O) n and solvent stabilization of SO 4 2– VDE ADE

Washington State University Pacific Northwest National Laboratory Calculated structures of SO 4 2- (H 2 O) n, n = 1-6

Washington State University Pacific Northwest National Laboratory PES of SO 4 2- (H 2 O) n, n = 4-40 Wang, Yang, Nicholas & Wang Science 294, 1322 (2001) Large hydrated clusters: a single sulfate dianion in the center of a water droplet

Washington State University Pacific Northwest National Laboratory Recent IR studies on SO 4 2- (H 2 O) n J. Chem. Phys. 125, (2006) Zhou, Santambrogio, Brummer, Moore, Woste, Meijer, Neumark & Asmis IR for n = 3-24 using FELIX at 17 K J. Am. Chem. Soc. 129, 2220 (2007) Bush, Saykally & Williams IR for n = 6 at OH stretching at 130 K

Washington State University Pacific Northwest National Laboratory Isomers of SO 4 2– (H 2 O) n J. Am. Chem. Soc. 129, 2220 (2007) Bush, Saykally & Williams Gao & Liu, J. Chem. Phys. 123, (2005)

Washington State University Pacific Northwest National Laboratory Dissociation of SO 4 2– (H 2 O) n for n = 3-17 (BIRD) Wong & Williams J. Phys. Chem. A 107, (2003) Two dissociation Channels: SO 4 2– (H 2 O) n → SO 4 2– (H 2 O) n-k + kH 2 O (1) → HSO 4 – (H 2 O) k + (H 2 O) m OH – (2) For n = 3, 4: (2) exclusively n = 5, 6: both (1) and (2), but for n = 5, (2) dominates, and for n = 6, (1) dominates n ≥ 7:(1) exclusively

Washington State University Pacific Northwest National Laboratory Size-dependent charge separation reactions of SO 4 2– (H 2 O) n for n = 3-7 Gao & Liu, J. Chem. Phys. 123, (2005)

Washington State University Pacific Northwest National Laboratory Second generation ESI-PES apparatus at low-temperatures 5 m

Washington State University Pacific Northwest National Laboratory The low-temperature ion trap Ion entranceIon exit Cold Head 10 K Rotatable

Washington State University Pacific Northwest National Laboratory

Washington State University Pacific Northwest National Laboratory Wang, Woo & Wang, J. Chem. Phys. 123, (2005) Hot bands Vibrationally-cold photoelectron spectrum of C 60 –

Washington State University Pacific Northwest National Laboratory Vibrationally resolved PES of cold C 70 - Chem. Phys. Lett. 233, 52 (1995) EA(C 70 ) = ± eV EA(C 60 ) = ± eV EA(C 60 ) = ± eV EA(C 70 ) = ± eV Too low!!!

Washington State University Pacific Northwest National Laboratory Photoelectron spectroscopy of cold C C C 70 - EA 2 (C 70 ) = ADE(C ) = 0.02 eV Wang, Woo, Huang, Kappes & Wang, Phys. Rev. Lett. 96, (2006)

Washington State University Pacific Northwest National Laboratory Electron-electron repulsion in C EA 1 (C 70 ) – EA 2 (C 70 ) = – = eV e 2 /r = 1.8 to 2.0 eV Wang, Woo, Huang, Kappes & Wang, Phys. Rev. Lett. 96, (2006)

Washington State University Pacific Northwest National Laboratory Acknowledgments Dr. Xue-Bin Wang Dr. Jie Yang Dr. Chuan-Fan Ding (Fudan U.) Dr. Xin Yang (Fudan U.) Dr. You-Jun Fu (U. Kentucky) Dr. Hin-Koon Woo (Scripps) Dr. Tom Waters (U. Melbourne) Supported by: DOE, NSF & Guggenheim Foundation Collaboration: J. B. Nicholas (theo) M. M. Kappes (fullerenes)