1. Jennifer Mann Indiana University Caroline Jarrold Group 67 th International Symposium on Molecular Spectroscopy June 18, 2012 Resonant two-photon detachment of WO 2 −

2. Introduction [1] M. Tulej, D. A. Kirkwood, G. Maccaferri, O. Dopfer, and J. P. Maier, Chem. Phys. 228 (1998) 293.; A. E. Bragg, J. R. R. Verlet, A. Kammrath, and D. M. Neumark, J. Chem. Phys. 121 (2004) 3515.; W. C. Lineberger and T. Patterson, Chem. Phys. Lett. 13 (1972) 40. ; M. Tulej, T. Pino, M. Pachkov, and J. P. Maier, Mol. Phys. 108 (2010) 865. ; T. Pino, M. Tulej, F. Guthe, M. Pachkov, and J. P. Maier, J. Chem. Phys. 116 (2002) 6126. [2] G. B. Griffin, A. Kammrath, O. T. Ehrler, R. M. Young, O. Cheshnovsky, and D. M. Neumark, Chem. Phys. 350 (2008) 69. [3] N. I. Hammer, R. N. Compton, L. Adamowicz, and S. G. Stepanian, Phys. Rev. Lett. 94 (2005) 153004.; C. Desfrançois, B. Baillon, J. P. Schermann, S. T. Arnold, J. H. Hendricks, and K. H. Bowen, Phys. Rev. Lett. 72 (1994) 48. [4] T. Andersen, K. R. Lykke, D. M. Neumark, and W. C. Lineberger, J. Chem. Phys. 86 (1987) 1858.; K. K. Murray, K. R. Lykke, and W. C. Lineberger, Phys. Rev. A 36 (1987) 699. Anion PE spectroscopy commonly used to characterize ground electronic states of anions Far fewer studies on excited states of anions Typically not bound relative to neutral + e − continuum Delocalized nature of high-lying electrons makes excited states difficult to characterize computationally Classes of anions where bound excited states are common Cumulenic carbon chains: C n −, C n H m −, and C 2n H − [1] Metal clusters: Hg n − [2] Molecules where neutral has a > 2 Debye dipole moment Dipole Bound State Bound by less than 100 cm −1 to the neutral + e − continuum e − bound in a delocalized orbital, does not perturb core Acetone, water-ammonia dimer [3] Transition-metal containing diatomics: PtN − FeO − [4] Current Study WO 2 − open shell, near degenerate d-like orbitals High electron affinity WO 2 3.5 Debye dipole moment

3. Resonant Two-Photon Detachment Anion Ground State Anion Excited State Neutral Ground State Detachment Continuum Photon Energy Electron counts EA Energy Q sym

4. Experimental Ions - laser ablation (532 nm) of W rod in pulse (30Hz) of UHP He Mass selected by time-of-flight WO 2 – intersected by a Nd:YAG pumped OPO (410 – 709 nm, 5 cm -1 resolution) Photodetached e − extracted by weak field (2 Vcm −1 ) up to dual MCP detector Ion signal, electron signal and laser power are sent to three gated integrators (SRS SR250) Absolute line positions within 28 cm -1 accuracy, relative spacings 7 cm -1

5. Computational Methods Density Functional Theory (DFT) Calculations Gaussian 09 Suite [1] B3LYP SDD pseudopotentials Triple-ζ Level aug-cc-PVTZ Time-dependent DFT (TDDFT) Electronic excitations predicted compared to experiment Excitations to high-lying orbitals not suitably treated by exchange functional CAM-B3LYP[2] - Coulomb-attenuated method combines hybrid B3LYP with long range correction Method, Basis Set advice provided by Raghavachari Group 1 M.J. Frisch et al., Gaussian 03, Revision D.01 (2004). 2 M.J. Frisch et al., Gaussian 09, Revision A.1 (2009). [1] M. J. T. Frisch, et. Al, Gaussian 09, Revision A.1 (Gaussian, Inc., Wallingford, CT, 2009). [2] T. Yanai, D. P. Tew, and N. C. Handy, Chem. Phys. Lett. 393 (2004) 51.

6. R2PD and PE Spectra R2PD Spectrum PE Spectrum EA PE spectrum Anion: 2 B 1 Neutral: 1 A 1 EA not definitively assigned ≤ 1.998 (10) eV 3 B 1 2 B 1, 320 cm -1 progression Significant portion of R2PD spectrum above detachment continuum R2PD bears resemblance to PE Spectrum G. E. Davico, R. L. Schwartz, T. M. Ramond, and W. C. Lineberger, J. Phys. Chem. A 103 (1999) 6167.

7. 1.8 1.92.02.12.22.32.4 Photon Energy (eV) Relative Electron Signal R2PD Spectrum 220 cm -1 890 cm -1 220 cm -1 944 cm -1 40 cm -1 56 cm -1 65 cm -1 B A Band A : Single peaks Transitions are doublet 2 B 1 Band B : Doublets Spin-forbidden quartet 2 B 1 W ζ(5d) = 2085 cm -1 Anion ground state E 1/2 Splitting is too small – not expected in doublet states Quartet states resolve into two E 1/2 sub-states Similar splitting (47 cm -1 ) seen in R2PI of Bi 3 [1] Assigned as transition from 4 A ʺ (E 3/2, E 5/2 ) 2 E ʺ (E 1/2 ) ν 1 symmetric stretch ν 2 bend * * * 1072 cm -1 823 cm -1 [1] C. A. Arrington and M. D. Morse, J. Phys. Chem. B 112 (2008) 16182. x10

8. Simulations of Bands A and B ∠ OWO(°) W − O (Å)ν 1 (cm -1 )ν 2 (cm -1 )ν 3 (cm -1 ) Anion 2B12B1 116.51.735965264898 4B14B1 130.01.768918222836 Neutral 1A11A1 104.51.68510723741014 3B13B1 113.41.7121017314945 ν 1 (cm -1 )ν 2 (cm -1 ) Band A 855255 Band B945229 Band B Band A s-wave 1.831 2.076 2.081 Anion structure Bond lengths and angles larger than neutral Lower vibrational frequencies Exp. Sim. Band A and B Frequencies are more consistent with anion Valence bound state

9. TDDFT Results Which electrons are involved in the excitation? Excitations below 3.7 eV involve HOMO and HOMO-1 Same orbitals as in the photoelectron spectrum Transitions to W-local unoccupied orbitals Multiconfigurational in nature Orbital description and transitions energies vary for method used Uncorrected B3LYP 26 states between 709 nm – 410 nm CAM-B3LYP (Coulomb attenuating method) [1] 11 states between 709 nm – 410 nm [1] T. Yanai, D. P. Tew, and N. C. Handy, Chem. Phys. Lett. 393 (2004) 51.

10. Photoelectron Spectrum R2PD Spectrum PE Spectrum EA Unoccupied orbitals 15a 1 14b 2 Anion Ground State, 2 B 1 Neutral Ground State, 1 A 1 16b 1 Neutral Excited State, 1 B 1 Neutral Excited State, 3 B 1

11. Conclusions R2PD of WO 2 – At least two distinct electronic states observed Assigned to valence bound states Bending and stretching frequencies similar to anion frequencies Doublet fine structure in Band B Spin forbidden quartet 2 B 1 transition Large spin-orbit splitting of W atom Quartet state resolves to two E 1/2 sub-states Diverging peaks in band B Mimics frequencies of neutral Coupling to a DBS? Unidentified peaks likely due to more than one additional electronic state TDDFT Need a more sophisticated level of theory? CASSCF, MRSDCI, FOCI, SOCI levels Generated potential curves and spectroscopic constants Transition metal containing carbides, WC [1] [1] K. Balasubramanian, J. Chem. Phys. 112 (2000) 7425.

12. Acknowledgements Prof. Caroline Jarrold Sarah Waller Raghavachari Group

14. Frequency anharmΔQΔQ Band A 22530.75 85520.40 Band B 22930.38 94530.10 PeakEnergy Spacing (cm - 1 ) AssignmentSpin-Orbit Splitting (cm -1 ) a0a0 00 a1a1 226 a2a2 218 a3a3 234 a4a4 0895 a5a5 169 a6a6 210 a7a7 218 a 8, b ʹ 0823 a9a9 210 a 10 210 a 11 202 b0b0 0040 b1b1 22640 b2b2 20256 b3b3 094465 b4b4 33965 Term symbol Relative energy (eV) 2B12B1 0.0 4B14B1 0.22 6Aʺ6Aʺ 4.21 1A11A1 2.04 3B13B1 2.18 5A25A2 4.62 Computational Results Anion Neutral

15. Current Study Resonant two-photon detachment Characterize anion bound states of transition metal containing oxides WO 2 − Neutral dipole moment: 3.53 Debye PE spectrum previously assigned by Lineberger[1] Anion: 2 B 1 Neutral: 1 A 1 C 2v symmetry Anion is open shell, many near degenerate 5d-like orbitals Observation of at least two different excited electronic states of WO 2 − Valence bound state Possibly some DBS character Spin allowed doublet doublet transition Spin-forbidden quartet doublet transition [1] G. E. Davico, R. L. Schwartz, T. M. Ramond, and W. C. Lineberger, J. Phys. Chem. A 103 (1999) 6167.

16. Doublets in Band B Band A Single peaks Transitions from 2 E 1/2 to excited doublet states W ζ(5d) = 2085 cm -1 Extended point group for selection rules For a S = 1/2 ground state, B 1 E 1/2 = E 1/2 WO 2 – ground state is doubly degenerate 2 E 1/2 Degeneracy broken by magnetic field or rotation (too small for our resolution!) Band B Doublet Peaks Quartet states (S = 3/2) resolve to two E 1/2 sub-states Arrington and Morse [1] Similar splitting (47 cm -1 ) seen in photon ionization of Bi 3 Assigned as transition from 4 A ʺ (E 3/2, E 5/2 ) 2 E ʺ (E 1/2 ) 16b 1 15a 1 14b 2 17a 1 B A [1] C. A. Arrington and M. D. Morse, J. Phys. Chem. B 112 (2008) 16182.

17. Introduction [1] P. J. Silva, R. A. Carlin, and K. A. Prather, Atmos. Environ. 34 (2000) 1811. [2] L. E. Hatch, J. M. Creamean, A. P. Ault, J. D. Surratt, M. N. Chan, J. H. Seinfeld, E. S. Edgerton, Y. X. Su, and K. A. Prather, Environ. Sci. Technol. 45 (2011) 5105. [3] M. Agundez, et al., Astron. Astrophys. 517 (2010) L2. Spectroscopic and computational studies characterizing cations far exceed that of anions Importance of negative ions increasingly evident Atmospheric: Silicates, phosphates,[1] organosulfates (ROSO 3 H)[2] Interstellar medium: C 6 H −, C 4 H −, C 8 H −, C 3 N −, C 5 N − and CN − [3] Negative ion photoelectron spectroscopy commonly used to characterize ground electronic states of anions Far fewer studies of excited states of anions Excited states typically not bound relative to neutral + e − continuum Delocalized nature of high-lying electrons makes excited electronic states of anions difficult to characterize computationally

18. 13 Anion doublet Anion quartet 17

19. Term symbol Relative energy (eV) 2B12B1 0.0 4B14B1 0.22 6Aʺ6Aʺ 4.21 1A11A1 2.04 3B13B1 2.18 5A25A2 4.62 Computational Results Anion Neutral