1. Electronic Structure of Oxyallyl Diradical: A Photoelectron Spectroscopic Study Takatoshi Ichino, Rebecca L. Hoenigman, Adam J. Gianola, Django H. Andrews, and W. Carl Lineberger JILA and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309 Weston T. Borden Department of Chemistry, University of North Texas Denton, TX 76203 Stephen J. Blanksby Department of Chemistry, University of Wollongong Wollongong, NSW 2522, Australia

2. Trimethylenemethane (TMM) vs Oxyallyl TMM diradicalOxyallyl diradical

3. TMM Diradical intermediate in thermal rearrangement of methylenecyclopropane (MCP) TMM diradical intermediate Hydrocarbon Thermal Isomerizations J.J. Gajewski, Academic Press, 1981 JACS 1982, 104, 967, Davidson and Borden

4. Trimethylenemethane (TMM) diradical 4  electrons TripletSinglet several ways to construct singlet wave functions 11 22 33 44 11 22 33 44

5. TMM triplet, singlet wave functions Triplet wave function 3 A 2 ′ ( 3 B 2 ) Singlet wave functions 1 E x ′ ( 1 B 2 ) 1 E y ′ ( 1 A 1 ) 1 A 1 ′ ( 1 A 1 ) HF energy 2h + J 23 – K 23 2h + J 23 + K 23 2h + J 22 – K 23 2h + J 22 + K 23 where J 22 − J 23 = K 23 sizeable exchange interaction triplet ground state (ESR measurements by Dowd, 1960’s)

6. Configuration interaction for 1 E x ′ TMM 1Ex′1Ex′ mixed with CI “allyl + p” reduction of electron repulsive interaction at the expense of  bonding energy  3 →  4 excitation  1 →  3 excitation JACS 1976, 98, 2695, Borden

7. Configuration interaction for 1 E y ′ TMM 1Ey′1Ey′ CI with  3 →  4 and  1 →  4 excitation CI “double bond + p + p” reduction of electron repulsive interaction at the expense of  bonding energy

8. Three lowest electronic states of TMM

9. Electron detachment from TMM anion EA (TMM) = 0.431 ± 0.006 eV E (X 3 A 2 ′ ― b 1 A 1 ) = 0.699 ± 0.006 eV CCC bend in 3 A 2 ′ : 425 ± 20 cm -1 in 1 A 1 : 325 ± 20 cm -1 JACS 1996, 118, 475, Wenthold et al. JACS 1994, 116, 6961, Wenthold et al.

10. Oxyallyl intermediates Thermal stereomutation of cyclopropanone Photochemistry of quadricyclanone JACS 1970, 92, 7488, Greene et al. JOC 1991, 56, 1907, Ikegami et al.

11. Oxygen substitution: Oxyallyl diradical JCS,PT2 1998, 1037, Borden et al. degeneracy of a 2 and 2b 1 lifted in oxyallyl

12. Hartree-Fock for non-degenerate system Triplet wave function 3B23B2 Singlet wave functions 1B21B2 1A11A1 1A11A1 energy h 2 + h 3 + J 23 – K 23 The ground state becomes 1 A 1 if J 22 − J 23 + K 23 < h 3 – h 2 h 2 + h 3 + J 23 + K 23 h 2 + h 3 + (J 22 + J 33 )/2 ± [K 23 2 + {h 2 -h 3 +(J 22 -J 23 )} 2 ] 1/2

13. Oxyallyl anion : O‾ + acetone reaction “M−H 2 ” ions “M−H” ion oxyallyl radical anion carbene radical anion acetone enolate anion

14. Photoelectron spectrum of M−H ion  radical  radical OH‾ + acetone reaction “M−H” acetone enolate JPC 1982, 86, 4873, Ellsion et al.

15. Photoelectron spectrum of M−H 2 and M−H ions O‾ + acetone reaction “M−H 2 ” “M−H”

16. Photoelectron spectrum of M−H 2 ion “M−H 2 ” detachment from O lone-pair orbitals

17. Photoelectron spectrum of M−H 2 ion X 1A1X 1A1 a 3B2a 3B2 EA = 1.945 ± 0.010 eVT e ( 3 B 2 ) = 0.056 ± 0.005 eV oxyallyl

18. Franck-Condon simulation for the 3 B 2 oxyallyl diradical B3LYP/6-311++G(d,p) calculations on 2 A 2 anion and 3 B 2 neutral CCC bending mode 400 ± 20 cm -1

19. Conclusions The 351 nm photoelectron spectrum of oxyallyl anion has been measured. The Franck-Condon fitting is successful for the transition from the 2 A 2 ground state of oxyallyl anion to the 3 B 2 state of oxyallyl, based on B3LYP/6-311++G(d,p) optimized geometries and normal modes. Vibrational progression is observed for a CCC bending mode of 400 ± 20 cm -1 in the 3 B 2 spectrum. Angular distributions of the photoelectrons from oxyallyl anion reveal an electronic state of oxyallyl to the lower electron binding energy side of the 3 B 2 spectrum. This is assigned to the 1 A 1 ground state of oxyallyl. The electron affinity of oxyallyl is 1.945 ± 0.010 eV, and the term energy for the 3 B 2 state is 0.056 ± 0.005 eV.

20. Acknowledgements Adam J. Gianola, Django H. Andrews, Rebecca L. Hoenigman, and W. Carl Lineberger, University of Colorado at Boulder Stephen J. Blanksby, University of Wollongong, Australia Weston T. Borden, University of North Texas NSF, AFOSR