1. The Negative Ion Photoelectron Spectra of MoV and CrV Presentedby Beau Barker

2. Introduction Ground states: V 4s 2 3d 3 Cr 4s 1 3d 5 Mo 5s 1 4d 5 Early transition metal dimers are of interest because d-electrons are involved in bonding. The d-orbitals are large enough to participate in bonding. Dimers containing later transition metals, such as CrCu, Cu 2 or Ni 2, are dominated by s  bonding.

3. NPES Basics: Electron Kinetic Energy (eKE) Electron Binding Energy (eBE) Experiments involve the use of the photoelectric effect: The eKE is measured and the eBE found from the difference in energy between the eKE and the photon: eBE is equal to the difference in energy between the anion and neutral states:

4. NPES Basics : Selection Rules Electronic State Transitions: For example: If anion is a doublet the neutral could be either a singlet or triplet.  Vibrational Transitions: Intensities of vibrational transitions are governed by Franck-Condon overlap between the anion and neutral species.

5. NPES Basics : Information from Spectra Electron affinity: The energy difference between the ground states of the anion and neutral. Vibrational frequencies: Found for both anion and neutral species. Anharmonicities: If known accurately these can also yield bond dissociation energies (for diatomics). Geometry Changes: Only the changes in equilibrium geometry are found between anion and neutral. Orbitals: Bonding characteristics of the detached electron.

6. NPES Basics : Generic Diatomic

7. Anion Photoelectron Spectrometer

8. Experimental Setup Metal diatomics are produced by creating a plasma around a V metal rod, and then adding Cr(CO) 6 or Mo(CO) 6. Spectra were taken with flow tube at room temperature. 52 Cr 51 V  and 92 Mo 51 V  were mass selected. About 25 pA of CrV  and 0.5 pA of MoV  were produced under these conditions.

9. Likely Electronic States Neutral: V 4s 2 3d 3 Cr 4s 1 3d 5 Mo 5s 1 4d 5 Anions: V 4s 2 3d 4 Cr 4s 2 3d 5 Mo 5s 2 4d 5 Excited state: V 4s 1 3d 4 2112 cm -1 Anion 1    d  2 d  4 d  4 s  2 3  : d  2 d  4 d  3 s  2 s  * 1 Neutral 2  : d  2 d  4 d  3 s  2 4  : d  2 d  4 d  3 s  1 s  * 1 2    d  2 d  4 d  4 s  1 4    d  2 d  4 d  2 s  2 s  * 1

10. Ground State of Neutrals Known Resonant two-photon ionization studies by Morse and co-workers have established the ground states and bond lengths of CrV and MoV. 1,2 2  2.5 d  2 d  4 d  3 s  2 CASSCF/CASPT2 by Andersson on CrV. 3 12 electronic states were calculated. The ground state agrees with experiment. The states are multiconfigurational. The configuration above is weighted at 57%. 1) Sickafoose, S. M.; Langenberg, J. D.; Morse, M. D. J. Phys. Chem. A 2000, 104, 3521. 2) Nagarajan, R.; Sickafoose, S. M.; Morse, M. D. J. Chem. Phys. 2007, 127, 014311. 3) K. Andersson. Theo. Chem. Acct. 2003, 110, 218 correct

11. DFT: MoV and CrV Gaussian 03 CrV BPW91/6-311+G(df) 1 MoV BPW91/SDD (Stuttgart-Dresden ECP) Various electronic states were explored. In order to find the ground state. States relevant to the photoelectron spectra are presented here. 1 ) Gutsev,G.L.; Mochena, M.D.; Jena, P.; Bauschlicher, C.W.; Partridge, H. J. Chem. Phys. 2004, 121, 6785.

12. MoV: 2.540 eV (488nm) Spectrum 2     3  3 2     1  + 2 12 1 High Binding Energy: 3 Transitions

13. MoV: Ground States 2    1   *=  2.5 *=  1.5 0-0 1-0 2-0 3-0 4-0 5-06-0 0-1 0-2 0-0 1-0 2-0 3-0 4-0 5-0 0-1 0-2 0-1

14. MoV: Ground States Anion: 1   d  2 d  4 d  4 s  2 to Neutral: 2  d  2 d  4 d  3 s  2 Detachment from d  Experimental Calculated EA 0.932 eV0.721 eV Δr e ± 0.063 Å0.115 Å  e Anion 578 cm -1 621 cm -1  e x e Anion -------------------  e Neutral 508 cm -1 407 cm -1  e x e Neutral 2.8 cm -1 ---------- SO  2.5-1.5 645 cm -1 ----------

15. MoV: First Excited Neutral x10 2 12 1 0-0 1-0 2-0 3-0 4-0 5-0 6-0 7-0 8-0 9-0 10-0

16. MoV: First Excited Neutral Anion: 1   d  2 d  4 d  4 s  2 to Neutral: 2   d  2 d  4 d  4 s  1 Detachment from s  Experimental Calculated T o 1.345 eV1.307 eV Δr e ±0.053 Å-0.019 Å  e Anion 572 cm -1 407 cm -1  e x e Anion -------------------  e Neutral 651 cm -1 533 cm -1  e x e Neutral 3.7 cm -1 ----------

17. MoV: Excited Anion State 2    3  3    0-0       0-1    0-0 1-0 2-0       1-0    0-0

18. MoV: Excited Anion State Anion: 3  d  2 d  4 d  3 s  2 s  * 1 to Neutral: 2  d  2 d  4 d  3 s  2 Detachment from s  * Experimental Calculated T 0 0.284 eV0.130 eV Δr e ± 0.040 Å -0.012 Å  e Anion --------- 393 cm -1  e x e Anion ------------------- SO  3-  2160 cm -1 ----------  e Neutral 508 cm -1 406 cm -1  e x e Neutral 2.8 cm -1 ----------

19. CrV: 514.5nm (2.409 eV) Spectrum * 2     3  3 2 332 33 4      3  3 High Binding Energy: 3 Transitions Spectra reproduced from Ph.D. thesis by Simson Alex 1997

20. CrV: Ground State (2.409 eV) x10 0-0 1-01-0 2-02-0 3-03-0 4-04-0 5-05-0 6-06-07-07-0 8-08-09-09-0 0-1 2    3  3

21. CrV: Ground State Spin-Orbit             2    3  3 0-0

22. CrV: Ground State Anion: 3  d  2 d  4 d  3 s  2 s  * 1 to Neutral: 2  d  2 d  4 d  3 s  2 Detachment from s  * Experimental Calculated * EA 0.521 eV 0.492 eV Δr e ± 0.03 Å-0.001 Å  e Anion 409 cm -1 491 cm -1  e x e Anion ------------------  e Neutral 520 cm -1 499 cm -1  e x e Neutral 7.2 cm -1 ---------- * DFT finds the 1   to be the anionic ground state; the 3  is 0.15 eV above it.

23. CrV: First Excited Neutral (2.409 eV) x5 2 332 33 0-0 1-0 2-0 3-0 4-0 5-0 6-0 * * * **** * ? ?

24. CrV: First Excited Neutral Anion: 3   d  2 d  4 d  3 s  2 s  * 1 to Neutral: 2   d  2 d  4 d  4 s  1 Two electron process Experimental Calculated T o 0.556 eV 0.301 eV Δr e ± 0.05 Å 0.123 Å  e Neutral 715 cm -1 875 cm -1  e x e Neutral 12.3 cm -1 ----------  e Anion 409 cm -1 491 cm -1

25. Summary The ground electron state of the anions, MoV  and CrV , were found to be different. MoV - 1  + vs. CrV - 3   The force constants for the  states are large. 1    d  2 d  4 d  4 s  2 2    d  2 d  4 d  4 s  1 MoV - 1  + 6.45Cr 2 1  g  3.54 1 MoV 2    8.19 Mo 2 1  g + 6.33 1 CrV 2   7.75Cu 2 1  g + 1.33 1 Units are mdyne/Å 1) Lombardi, J. R.; Davis, B. Chem. Rev. 2002, 102, 2431.

26. Thanks Doreen Leopold advisor Simson Alex for CrV experimental data Minnesota Supercomputing Institute Research Corporation

27. CrV: Ground State Spin-Orbit The uneven spin-orbit spacing in the anion 3  implies the existence of a low lying excited state; not seen in the spectrum. State Spacing Neutral  2.5-  1.5 270 cm -1 Anion  3-  270 cm -1 Anion  2-  1335 cm -1

28. Spin-Orbit States Can have spin-orbit transition when orbital angular momentum is not 0. Using a simple first order approach the spin- orbit states should be evenly spaced by A. E so =A  A is negative so highest  state is lowest. MoVCrV 3   427 cm -1 210 cm -1  = 3,2,1 2   854 cm -1 420 cm -1  = 2.5,1.5

29. MoV: High Binding Energy

30. CrV: Second Excited Neutral (2.409 eV) 0-0 4    3  3 1-0 2-0 3-0 4-0 0-1

31. CrV: Second Excited Neutral (2.409 eV)  Anion: 3   d  2 d  4 d  3 s  2 s  * 1 to Neutral: 4   d  2 d  4 d  3 s  1 s  * 1  Detachment from a d  Experimental Calculated T o 1.143 eV N/A Δr e 0.05 Å N/A  e Neutral 440 cm -1 N/A  e x e Neutral <4.0 cm -1 N/A  e Anion 409 cm -1 491 cm -1

32. CrV High Binding Energy (2.601eV) 4    CrV  * 0-0 1-0 2-0 3-0 433433 0-0 1-0 2-0 3-0 4-0 5-0 4    3  3 0-0 1-0 2-0 0-1