The cylcopentadienyl radical revisited: the effects of asymmetric deuteration of Jahn-Teller molecules Samantha Strom, Jinjun Liu Department of Chemistry.

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Presentation transcript:

The cylcopentadienyl radical revisited: the effects of asymmetric deuteration of Jahn-Teller molecules Samantha Strom, Jinjun Liu Department of Chemistry University of Louisville June 19, 2012

LOUISVILLE.EDU  Introduction: Motivation & Goals  Theory  “Experimental” Spectra  Spectral Analysis & Results  Conclusion Outline

LOUISVILLE.EDU  Jahn-Teller (JT) effect- occurs to non- linear polyatomic molecules in orbitally degenerate electronic states  Pseudo-Jahn-Teller (PJT) effect- occurs between two (or several) electronic states that are usually close in energy  Both JT & PJT effects: o Distort the geometry o Lower the molecular symmetry o Decrease the total vibronic energy  JT & PJT molecules are in fluxional motion such as a pseudo-rotation around the Conical Intersection (CI) Jahn-Teller & Pseudo-Jahn-Teller Effects  Jahn-Teller Potential Energy Surface  Pseudo-Jahn-Teller Potential Energy Surface

LOUISVILLE.EDU  PJT-active molecules can be formed from asymmetric substitution of deuteriums, halogens, or methyl groups for hydrogen atoms of JT-active molecules Asymmetric Deuteration  Electronic PESs remain unchanged upon partial or asymmetric deuteration  Vibrational modes and their harmonic frequencies are altered  Vibronic symmetry is lowered whereas electronic symmetry remains the same  Vibrational effect can be separated from vibronic effect Asymmetric Substitution: JT  PJT

LOUISVILLE.EDU Cyclopentadienyl Radical (cp)  Experimental o Laser Induced Fluorescence (LIF)  L. Yu, J.M. Williamson, and T.A. Miller, Chem. Phys. Lett. 162, 431 (1989).  L. Yu, D.W. Cullin, J.M. Williamson, and T.A. Miller, J.Chem. Phys. 98, 2682 (1993). o Dispersed Fluorescence (DF)  B.E. Applegate, A.J. Bezant, and T.A. Miller, J. Chem. Phys. 114, 4869 (2001). o Pulsed-Field Ionization Zero-Kinetic Energy (PFI-ZEKE)  H.J. Wörner, F.Merkt, Angew. Chem. Int. Ed. 45, 293 (2006)  H.J. Wörner, F. Merkt, J.Chem. Phys. 127, (2007).  Computational  M.J. Bearpark, M.A. Robb, and N. Yamamoto, Spectrochim. Acta A 55, 639 (1999).  B.E. Applegate, T.A. Miller, T.A. Barckholtz, J. Chem. Phys. 114, 4855 (2001). C 2v (e x ) C 2v (e y ) D 5h 1.H.J. Wörner and F. Merkt, J. Chem. Phys. 126, (2007). 2.L. Yu, D.W. Cullin, J.M. Williamson, and T.A. Miller, J. Chem. Phys. 98, 2682 (1993).

LOUISVILLE.EDU Asymmetric deuteration C5H4DC5H4DC5H4DC5H4D C5H5/C5D5C5H5/C5D5C5H5/C5D5C5H5/C5D5 C 5 HD 4 1. L. Yu, D.W. Cullin, J.M. Williamson, and T.A. Miller, J. Chem. Phys. 98, 2682 (1993). 2. L. Yu, S.C. Foster, J.M. Williamson, M.C. Heaven, and T.A. Miller, J. Chem. Phys. 92, 4263 (1988). C 5 H 4 D-10K C 5 HD K C 5 H 5 -3K

LOUISVILLE.EDU  Reinvestigate the previous experimental spectra with a new model 1,2, which simulates the two vibronic bands simultaneously  Resolve the discrepancy between experimentally determined and ab initio calculated Jahn-Teller distorted geometries Goals Expt. Ref 1 Expt. Ref 2 Calculated Ref 3 Calculated Ref 4 R CC (2)1.421 (1) ΔR CC ( 2 B 1 ) N/A (5)0.066 ΔR CC ( 2 A 2 ) N/A (5) References 1.L. Yu, J.M. Williamson, and T.A. Miller, Chem. Phys. Lett. 162, 431 (1989). 2.L. Yu, D.W. Cullin, J.M. Williamson, and T.A. Miller, J. Chem. Phys. 98, 2682 (1993). 3.M.J. Bearpark, M.A. Robb, and N. Yamaoto, Spectrochim. Acta A 55, 639 (1999). 4. B.E. Applegate, T.A. Miller, and T.A. Barckholtz, J. Chem. Phys. 114, 4855 (2001). 1.D.Melnik, J. Liu, R.F. Curl, and T.A. Miller, Mol. Phys. 105, 529 (2007). 2.D. Melnik, J. Liu, M.W. Chen, and T.A. Miller, J. Chem. Phys. 135, (2011). CH 2 DOCHD 2 O CH 3 O CD 3 O Methoxy

LOUISVILLE.EDU  Introduction: Motivation & Goals  Theory o Hamiltonian o Intensity Formula & Selection Rules  “Experimental” Spectra  Spectral Analysis & Results o Molecular Constants o Geometry Determination  Conclusion Outline

LOUISVILLE.EDU Basis Set  - vibronic basis functions;  J - total angular momentum of the molecule;  P - projection of J onto the molecule-fixed z or c axis;  M - projection of J onto the space-fixed Z or “C” axis;  S = 1/2 - spin of electron;  Σ=±1/2 - projection of S onto the z or c axis;  =±1 - parity of the basis functions with respect to the σ zx reflection. y x z σ zx For cp:

LOUISVILLE.EDU Effective Hamiltonian H Q = Vibronic Degeneracy Lifting H rot = rotational H rot,corr = “spin uncoupling” 1,2 H cor = Coriolis Interaction H JT = Jahn-Teller Distortion 1.J.T. Hougen, J. Mol. Spect. 81, 73 (1980). 2.Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122 (1984). Hougen Operator 1 -

LOUISVILLE.EDU Hamiltonian Elements

LOUISVILLE.EDU Transition Intensity Formula For transitions from the Σ=1/2 levels: For transitions from the Σ=-1/2 levels: 1.L. Yu, D.W. Cullin, J.M. Williamson, and T.A. Miller, J. Chem. Phys. 98, 2682 (1993). Nuclear Spin Statistics weights of rovibronic levels a : Vibronic Species 2A22A22A22A2 2B12B12B12B1 C5H4DC5H4DC5H4DC5H4D K a /K c b e/e or e/o o/e or o/o e/e or e/o o/e or o/o 5335 C 5 HD 4 K a /K c b e/e or o/o e/o or o/e e/e or o/o e/o or o/e 5445 a- K a and K c are the projections of the angular momentum N along inertial a and c axes, respectively b- The e and o indicate whether K a /K c is an even or odd integer Selection Rules:

LOUISVILLE.EDU “Experimental” Spectra Yu et al. (1993) Cold- 3K Hot- 10K ΔEΔE L. Yu, D.W. Cullin, J.M. Williamson, and T.A. Miller, J. Chem. Phys. 98, 2682 (1993).

LOUISVILLE.EDU Simulated Spectra: Asymmetric Top Model- C 5 H 4 D V. Stakhursky and T.A. Miller, 56 th International Symposium of Molecular Spectroscopy (The Ohio State University, Columbus Ohio, 2001). Hot- 10K Cold- 3K a-type b-type b-type b-type Simulation Simulation Experimental Experimental

LOUISVILLE.EDU Simulated Spectra: New Model V. Stakhursky and T.A. Miller, 56 th International Symposium of Molecular Spectroscopy (The Ohio State University, Columbus Ohio, 2001). C 5 HD 4 C5H4DC5H4DC5H4DC5H4D

LOUISVILLE.EDU Molecular Constants: One set of constants for both levels! C 5 H 5 (a) C5H4DC5H4DC5H4DC5H4D C 5 HD 4 C 5 D 5 (a) Ground State B zz (C) (65) (62) (B xx +B yy )/ (96) (84) (79) (132) (B xx -B yy )/ (111) (103) B zz ζ t (Cζ t ) (102) (651) (737) (165) h1h1h1h (27) (87) (86) (37) ΔEΔEΔEΔE (15) (15) ζtζtζtζt Excited State B zz (C) (59) (58) (58) (105) (B xx +B yy )/ (86) (71) (73) (126) (B xx -B yy )/ (7) (6) Te (1) (1) # transitions σ h 1 – Jahn-Teller distortion ΔE- Vibronic Degeneracy Lifting L. Yu, J.M. Williamson, and T.A. Miller, Chem. Phys. Lett. 162, 431 (1989). (a) L. Yu, J.M. Williamson, and T.A. Miller, Chem. Phys. Lett. 162, 431 (1989). Unit: GHz ζ t - Coriolis Constant

LOUISVILLE.EDU Rotational Constants & JT distortion constants (h 1 ) JT distortion constants (h 1 ) B xx, B yy, B zz – Rotational constants for the undistorted Geometry h 1 – Jahn-Teller distortion constant h 2 – second order Jahn-Teller distortion constant (zero for cp) Φ- angle of pseudorotation for the molecule in the moat around the CI Φ=0 Φ=πΦ=πΦ=πΦ=π 1. J.k.G. Watson, J. Mol. Spectros (1984)

LOUISVILLE.EDU Geometry Determination 2 B 1 (e x ) 2 E 1 ’’ 2 A 2 (e y ) C 1 -C 2 (Å) (8) R cc 0 (Å) (10) C 1 -C 2 (Å) (8) C 2 -C 3 (Å) (21) R CH (Å) (46) C 2 -C 3 (Å) (21) C 3 -C 4 (Å) (26) ΔR CC (Å) (26) C 3 -C 4 (Å) (26) C-H Bonds (Å) (46) C-C-C Bond Angles (deg) 108 C-H Bonds (Å) (46) Θ 3 (C 2 -C 3 -C 4 ) (deg) (58) H-C-C Bond Angles (°) 126 Θ 3 (C 2 -C 3 -C 4 ) (deg) (60) Θ (C1-C2-H2) (deg) (40) Θ (C1-C2-H2) (deg) (57) Θ (C2-C3-H3) (deg) (26) Θ (C2-C3-H3) (deg) (29) C1C1 C2C2 C3C3 C4C4 C5C5 H2H2 H3H3 H1H1 H5H5 H4H4 C1C1 C2C2 C3C3 C5C5 C4C4 H1H1 H2H2 H3H3 H4H4 H5H5 k=

LOUISVILLE.EDU Comparison with previous works This WorkExpt. Ref 1 Expt. Ref 2 Calc. Ref 3 Calc. Ref 4 R CC (10) (2)1.421 (1) ΔR CC (e x )0.021 (26)N/A (5)0.066 ΔR CC (e y ) (26)N/A (5) R CH (46)1.083 (1)1.073 (5)N/A1.072 References 1.L. Yu, J.M. Williamson, and T.A. Miller, Chem. Phys. Lett. 162, 431 (1989). 2.L. Yu, D.W. Cullin, J.M. Williamson, and T.A. Miller, J. Chem. Phys. 98, 2682 (1993). 3.M.J. Bearpark, M.A. Robb, and N. Yamaoto, Spectrochim. Acta A 55, 639 (1999). 4. B.E. Applegate, T.A. Miller, and T.A. Barckholtz, J. Chem. Phys. 114, 4855 (2001). Unit: Å (angst.)

LOUISVILLE.EDU   Previous experimental spectra of the two asymmetrically deuterated isotopomers of the cyclopentadienyl radical have been successfully simulated using a spectroscopic model that describes the two zero point levels of the ground electronic state using one set of molecular parameters.  The model reproduces the lifting of vibronic degeneracy and the Jahn-Teller distortion.  Based on the experimentally derived rotational constants and the Jahn-Teller constants, the undistorted and distorted geometries of the cyclopentadienyl radical have been determined, which can be used to benchmark quantum chemistry calculations. Conclusion

LOUISVILLE.EDU Advisor Dr. Jinjun Liu Group Members  Hui Liu  Dustin Cummings  Bokhodir S. Mamedov  Malika S. Rizmanova Collaborator Dr. Terry A. Miller Acknowledgements

LOUISVILLE.EDU C1C1 C2C2 C3C3 C5C5 C4C4 H1H1 H2H2 H3H3 H4H4 H5H5 Geometry Determination C1C1 C2C2 C3C3 C4C4 C5C5 H2H2 H3H3 H1H1 H5H5 H4H4 2 E 1 ’’ R cc 0 (Å) (10) R CH (Å) (46) ΔR (Å) (26) C-C-C Bond Angles (deg) 108 H-C-C Bond Angles (°) A 2 (e y ) C 1 -C 2 (Å) (8) C 2 -C 3 (Å) (21) C 3 -C 4 (Å) (26) C-H Bonds (Å) (46) Θ 3 (C 2 -C 3 -C 4 ) (deg) (60) Θ (C1-C2-H2) (deg) (57) Θ (C2-C3-H3) (deg) (29) 2 B 1 (e x ) C 1 -C 2 (Å) (8) C 2 -C 3 (Å) (21) C 3 -C 4 (Å) (26) C-H Bonds (Å) (46) Θ 3 (C 2 -C 3 -C 4 ) (deg) (58) Θ (C1-C2-H2) (deg) (40) Θ (C2-C3-H3) (deg) (26)