Large Amplitude Motions: Revealing Information Transfer

Präsentation zum Thema: "Large Amplitude Motions: Revealing Information Transfer"—  Präsentation transkript:

1 Large Amplitude Motions: Revealing Information Transfer
Along Conjugated Systems Jens-Uwe Grabow, Hilkka Saal, Isabelle Kleiner, Angela R. Hight-Walker, Jon T. Hougen und Walther Caminati Institut für Physikalische Chemie & Elektrochemie National Institute of Standards and Technology – Gaithersburg, MD Dipartimento di Chimica “G.Ciamician” Universita’ di Bologna

2 Benzotrifluoride: V6 internal rotation
Torsion  Rotation Centrifugal Distorsion Torsion Rotation Interaction

3 Benzotrifluoride: V6 internal rotation barrier with 7 digit accuracy
the heavy-top case of benzotrifluride: A v=2 A E v=1 E A v=0 barrier to internal rotation V6 = (3) cm-1 Vadim V. Ilyushin, Laura B. Favero, Walther Caminati, Jens-Uwe Grabow, ChemPhysChem, accepted.

4 Coaxial oriented Beam-Resonator Arrangement (COBRA)
Impulse FID resonator tuning Fabry-Perot resonator FT polarization pulse: coherence between rotating molecular dipoles oscillating macroscopic dipole moment: electromagnetic field at frequencies of molecular transitions

5 “coaxially oriented beam resonator arrangement“ (COBRA) FTMW-Spectrometer

6 Information Transfer Through Conjugated bonds?
para-tolualdehyde: Information Transfer Through Conjugated bonds? Top view: Side view: along internal rotation axis 3 aldehyde group introduces asymmetry: 2 H 1 2 1 C O 1 3 3 2 Will the methyl group know about the asymmetry? V6 vs. V3 barrier to internal rotation Walther Caminati, Angela R. Hight-Walker, Jon T. Hougen, Isabelle Kleiner, Hilkka Saal, Jens-Uwe Grabow, to be published.

7 Internal rotation: Permutation-Inversion (PI) group theoretical considerations
-CH3 top: C3 permutation-inversion symmetry: C3 -C6H4-CHO frame: Cs point group symmetry: E,  Molecular symmetry group: G6 H1 C3 axis H2 H3 2 C3 group H 1 C C3 E C3² (123) (123)² = (132) A1 1  * O 3 H. C. Longuet-Higgins, Mol. Phys. 6 (1963), 445. J. T. Hougen, J. Chem. Phys. 37 (1962), 1433; J. Chem. Phys. 39 (1963), 358.

8 H1 H2 H3 tunnel-pathways, tunnel-Hamilton matrix,
energy level split diagram K=0, vt=0 Htunneling: rotation of CH3-group H1 C3 axis E1 H2 H3 Htunneling J0J 3 (feasible) equivalent tunneling pathways in total: H11 HE HE H11 HE 2Htunneling H11 symmetric matrix, 2 eigenvalues: W1= W(A1)=H11+2HE W2=W3=W(E1)=H11-HE A1 Γ(G6)

9 V6/V3- torsional barrier
perfect fit to torsional ground state (vt=0) spectrum archieved for different contributions to the barrier

10 free internal rotor – high barrier torsion
gi = 2 gi = 3 E |m| = 4 E vt = 2 A |m| = 3 A vt = 1 E |m| = 2 E vt = 0 |m| = 1 A m = 0 ∞ V

11 “free jet“ (FJ) absorption mm-wave setup
Side View Top View

12 “free jet“ (FJ) Absorptions-Millimeterwellen-Spektrometer

13 FJ-A-MMW vs. COBRA-FT-MW spectrometer

14 para-tolualdehyde: J = 34  33 a R-band
T  50 K required broken diffusion pump heaters!

15 low-barrier torsional energy level diagram

16 reduced energy level diagram for m = +/- 3
para-tolualdehyde: reduced energy level diagram for m = +/- 3 E – (1/2)(B+C)J(J+1)

17 Information Transfer Through Conjugated bonds!
para-tolualdehyde: Information Transfer Through Conjugated bonds! nlm CONSTANT OPERATOR VALUE STD DEV 202 A B C DAB 211 RHORHO 220 F V 404 DJ DJK DK ODELN ODELK 413 ALV AK ODELTA C 422 GV AK DELTA C FV ODAB 431 AK 440 V AK 642 AMV BK C DELTAB result of global fit to ~800 transitions in 5 different torsional states at experimental accuracy

18 Information Transfer Through Conjugated bonds!
para-tolualdehyde: Information Transfer Through Conjugated bonds! Top view: Side view: along internal rotation axis 3 2 H 1 2 1 C O 1 3 3 2 the methyl group does know about the orientation of the aldehyde group hiding in the plane - but not from sterical hindering! barrier to internal rotation: V3 = 28.3 >> V6 = 5.3 cm-1

19 Acknowledgement Deutsche Forschungsgemeinschaft (DFG)
Land Niedersachsen Deutscher Akademischer Austauschdienst (DAAD) Università di Bologna Minister of Education, Italy