1. Theoretical Studies of Observable Transitions to Recoupled Pair Bonded States of Sulfur Halide Compounds Jeff Leiding, D. E. Woon, T. H. Dunning, Jr. University of Illinois SF/SCl, SF 2 /SFCl/SCl 2

2. Motivation for Current Work SF 2 : Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2009, 113, 7915. SFCl: Leiding, J.; Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2011, 115, 329. SCl 2 : Leiding, J; Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2011, 115, 4757. a4Σ-a4Σ- X2ΠX2Π σ*π*

3. Motivation for Current Work SF 2 : Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2009, 113, 7915. SFCl: Leiding, J.; Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2011, 115, 329. SCl 2 : Leiding, J; Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2011, 115, 4757. a4Σ-a4Σ- X2ΠX2Π σ*π* Spin-forbidden

4. Motivation for Current Work SF 2 : Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2009, 113, 7915. SFCl: Leiding, J.; Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2011, 115, 329. SCl 2 : Leiding, J; Woon, D. E.; Dunning, T. H., Jr. J. Phys. Chem. A 2011, 115, 4757. a4Σ-a4Σ- A2Σ-A2Σ- X2ΠX2Π σ*π* Spin-forbidden Spin-allowed

5. Methods CASSCF/MRCI+Q aug-cc-pV(5+d)Z for diatomics aug-cc-pV(Q+d)Z for triatomics Transform CAS orbitals into GVB orbitals: singly occupied, atom-centered CASSCF: Complete active space self-consistent field MRCI: Multireference configuration interaction GVB: Generalized valence bond

6. Low-Lying States of SCl SCl(a 4 Σ - ) SCl(X 2 Π )

7. Low-Lying States of SCl SCl(a 4 Σ - ) SCl(X 2 Π )

8. Low-Lying States of SCl SCl(a 4 Σ - ) SCl(X 2 Π ) No experimental data for excited states of SCl/SF

9. Covalent SCl(X 2 Π ) GVB Orbitals

10. SCl(a 4 Σ - ) GVB Orbitals

11. Recoupled SCl( 2,4 Σ - ) GVB L GVB R r e ( 4 Σ - ) orbs 2,4 Σ - orbs coupled MO/GVB

12. Recoupled SCl( 2,4 Σ - ) antibonding GVB L GVB R r e ( 4 Σ - ) orbs 2,4 Σ - orbs coupled MO/GVB 4 Σ - : “Recoupled pair bond”

13. Recoupled SCl( 2,4 Σ - ) antibonding GVB L GVB R r e ( 2 Σ - ) orbs r e ( 4 Σ - ) orbs 2,4 Σ - orbs coupled MO/GVB 2 Σ - : “Frustrated recoupled pair bond” 4 Σ - : “Recoupled pair bond”

14. Low-Lying Triatomic States SX( 2 Π ) SX( 2 Σ - ) 1.Li et al. J. Phys. Chem. A 1998, 102, 7233. 2.Colton et al. J. Elec. Spec. Relat. Phenom. 1974, 3, 345. 3.Gholivand, K. et al. Phosphorus, Sulfur and Silicon, 1996, 1, 269.

15. Low-Lying Triatomic States SX 2 ( 1 A 1 ) SX( 2 Π ) SX( 2 Σ - ) 1.Li et al. J. Phys. Chem. A 1998, 102, 7233. 2.Colton et al. J. Elec. Spec. Relat. Phenom. 1974, 3, 345. 3.Gholivand, K. et al. Phosphorus, Sulfur and Silicon, 1996, 1, 269.

16. Low-Lying Triatomic States SX 2 ( 1 A 1 ) SX 2 ( 1 B 1 ) SF 2 singly occupied orbitals SF 2 ( 1 B 1 ) SX( 2 Π ) SX( 2 Σ - ) T e, T v (eV) 1.Li et al. J. Phys. Chem. A 1998, 102, 7233. 2.Colton et al. J. Elec. Spec. Relat. Phenom. 1974, 3, 345. 3.Gholivand, K. et al. Phosphorus, Sulfur and Silicon, 1996, 1, 269. 2.3

17. Low-Lying Triatomic States SX 2 ( 1 A 1 ) SX 2 ( 1 B 1 ) SX 2 ( 1 A 2 ) SF 2 singly occupied orbitals SF 2 ( 1 A 2 ) SF 2 ( 1 B 1 ) SX( 2 Π ) SX( 2 Σ - ) T e, T v (eV) 1.Li et al. J. Phys. Chem. A 1998, 102, 7233. 2.Colton et al. J. Elec. Spec. Relat. Phenom. 1974, 3, 345. 3.Gholivand, K. et al. Phosphorus, Sulfur and Silicon, 1996, 1, 269. 2.3 0.7

18. Low-Lying Triatomic States SX 2 ( 1 A 1 ) SX 2 ( 1 B 1 ) SX 2 ( 1 A 2 ) SF 2 singly occupied orbitals SF 2 ( 1 A 2 ) SF 2 ( 1 B 1 ) SX( 2 Π ) SX( 2 Σ - ) T e, T v (eV) 1.Li et al. J. Phys. Chem. A 1998, 102, 7233. 2.Colton et al. J. Elec. Spec. Relat. Phenom. 1974, 3, 345. 3.Gholivand, K. et al. Phosphorus, Sulfur and Silicon, 1996, 1, 269. 2.3 0.7

19. SFCl Bond-Stretch Isomers F-recoupled Cl-recoupled SFCl(A 1 A ″ ): Minima on same PES

20. SFCl Bond-Stretch Isomers Singly occupied orbitals ∆E=9.0 kcal/mol 1.594 Å θ=86.9º 2.421 Å 1.912 Å 1.962 Å θ=88.5º F-recoupled Cl-recoupled SFCl(A 1 A ″ ): Minima on same PES (PES for a 3 A ″ )

21. SFCl Bond-Stretch Isomers Singly occupied orbitals ∆E=9.0 kcal/mol 1.594 Å θ=86.9º 2.421 Å 1.912 Å 1.962 Å θ=88.5º We predict observable signature of bond-stretch isomerism due to recoupled-pair bonding: “ 1 A 2 ” line will split. F-recoupled Cl-recoupled f e =oscillator strength Energies (eV) SFCl(A 1 A ″ ): Minima on same PES (PES for a 3 A ″ )

22. Conclusions 1.RPB exhibited in low-lying states of SF/SCl and SF 2 /SFCl/SCl 2 2.Understand excited state behavior via RPB model 3.Good agreement of excited state observables with experiment 4.Predictions for excited states of SF/SCl and SF 2 /SFCl/SCl 2 5.Possibility of observing electronic signature of bond-stretch isomers in SFCl via electronic spectroscopy

23. Acknowledgements Professor Thom Dunning Dr. David Woon Dr. Lina Chen Dunning Group Funding: NCSA, Distinguished Chair for Research Excellence in Chemistry

24. Low-Lying triatomic states (T e ) SX 2 ( 1 A 1 ) SX 2 ( 1 B 1 ) SX 2 ( 1 A 2 )

25. Low-Lying triatomic states (T e ) Excitation energies (kcal/mol) Singlet-Triplet gap (kcal/mol) 52.9 20.3 16.2 SCl 2 SF 2 50.2 14.5 18.5 13.3 20.0 SX 2 ( 1 A 1 ) SX 2 ( 1 B 1 ) SX 2 ( 1 A 2 )

26. Relaxed geometries 1 A 1 geometries SCl 2 ( 1 B 1 )SF 2 ( 1 B 1 ) unfavorable Low-Lying triatomic states (T v,T e ) Molecule StateMethodTeTe TvTv SF 2 1B11B1 Theo53.0119.3 1A21A2 Theo69.182.0 SCl 2 1B11B1 Theo50.278.4 1A21A2 Theo70.383.3