THE PHENALENYL FREE RADICAL A JAHNTELLERHERZBERGTELLER D 3

THE PHENALENYL FREE RADICAL A JAHN-TELLER-HERZBERG-TELLER D 3 H PAH G. D. O’CONNOR, T. P. TROY, D. A. ROBERTS, N. CHALYAVI, B. FÜCKEL, M. J. CROSSLEY, K. NAUTA, J. F. STANTON and T. W. SCHMIDT

Diffuse Interstellar Bands 10% of light missing at this wavelength Hobbs et al a catalog of diffuse interstellar bands in the spectrum of HD 204827 due to gas phase molecules… what are they?

Interstellar Carbon The “Unidentified Infrared Bands” - believed due to aromatic material in Interstellar medium. Aromatic material?

Kwok, Nature 430, 895 (2004)

Cosmic “dust” and RSRs (Resonance-Stabilized Radicals) Hydrogenated Amorphous Carbon (HAC) S. Kwok. Nature 2004, 430, 985– 991.

Synthetic chemistry High Voltage Discharge ` ` -H phenalene phenalenyl

R 2 C 2 PI Spectrum (D 1 ← D 0) 19560 cm-1 (+760 cm-1) m/z=165

Comparison with the DIBs

R 2 C 2 PI Spectrum (D 1 ← D 0) 19560 cm-1 (+760 cm-1) m/z=165

Typical origin-dominated spectrum 21200 19400 20400

Dispersed Fluorescence of Origin -1 +810 cm 807 cm-1

Dispersed Fluorescence of +760 cm-1 +1590 cm-1 Behaves like vibrational modes … look for gradient in transition moment

13 p-electrons Cation is 12 p electron aromatic (breaks Hückel rule)

Frontier Orbitals e” D 3 h a 1” e”

Coulson’s Pairing 22 E” 21 A 1’ 4 one-electron excitations gives 4 states: 2 pairs of E”

Symmetry considerations Electronic transition allowed (in-plane) Vibronic transition allowed (in-plane) e’ modes allowed (in-plane) a 1’ modes allowed (in-plane)

CCSD pvdz calculations Ground state modes near 810 cm-1 Mode Sym Freq cm-1 31 a 2'' 784. 62 6 a 1 ' 785. 65 25 28 e' a 1'' 828. 32 851. 19

R 2 C 2 PI Spectrum (D 1 ← D 0) 19560 cm-1 (+760 cm-1) m/z=165

n 25 e’ vibrational modes Qa Qb

p/2 p 2 p 3 p/4

Adiabatic representation Nuclear Kinetic Electronic Which is great when we can ignore off-diagonal KE terms…

Move to the diabatic representa . . .

Jahn-Teller diabatic Hamiltonian Harmonic potential Jahn-Teller Effect of Jahn-Teller matrix on n 25? n =1 ~4 cm-1

Effect on the spectrum? Still origin dominated! x 50 Frequency (cm-1)

Transition moment suggests coupling to 2 E” levels 22 E” |5> |4> m=2. 5 21 E” |2> |3> m=0. 06 21 A 1’ |1> In diabatic representation, this is a manifestation of pseudo-Jahn-Teller (Herzberg-Teller) coupling

Transition moment suggests coupling to 2 E” levels 22 E” |5> |4> m=2. 5 21 E” |2> n=0 |3> m=0. 06 21 A |1> 1’ Jahn-Teller Pseudo Jahn-Teller

More or less solved? Excitation spectrum CCSD Simulation (Stanton) Experiment EOM-CCSD/p. JT

People and Money G. O’Connor Dr K, Nauta Dr B. Fückel Prof. John F. Stanton Prof. M. J. Crossley Dr Tyler P. Troy Dr Nahid Chalyavi Derrick Roberts Australian Research Council