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Large Amplitude Motions:

Revealing Information TransferAlong Conjugated Systems

Jens-Uwe Grabow, Hilkka Saal, Isabelle Kleiner,

Angela R. Hight-Walker, Jon T. Hougen und Walther Caminati

Dipartimento di Chimica “G.Ciamician” Universita’ di Bologna

Institut für Physikalische Chemie & Elektrochemie

National Institute of Standards and Technology – Gaithersburg, MD

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4362

1232

132

126

2int

2222224224

2222

62

int

6sin},{3cos},{}3sin,{6cos

)}(,{)(2

)2

()(22

2)6cos1(2

1

pFpPPPVpPPPPDpPPVpPFH

PPPPPPPPPPH

PCB

APPCB

PCB

H

pFPVFpH

HHHHH

mamcbbcaJbaabccJJ

cbaKcbJaKaJKJcd

aeffcbR

aT

cdRT

Benzotrifluoride: V6 internal rotation

Torsion

Rotation

Centrifugal Distorsion

Torsion Rotation Interaction

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Benzotrifluoride: V6 internal rotation barrier with 7 digit accuracy

barrier to internal rotation V6 = 3.229948(3) cm-1

Vadim V. Ilyushin, Laura B. Favero, Walther Caminati, Jens-Uwe Grabow,

ChemPhysChem, accepted.

the heavy-top case of benzotrifluride:

A

A

A

E

Ev=0

v=1

v=2

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Coaxial oriented Beam-Resonator Arrangement (COBRA)

Fabry-Perot resonator

resonatortuning

FT

FID

Impulse

polarization pulse:

coherence between

rotating molecular dipoles

oscillating macroscopic

dipole moment:

electromagnetic field at frequencies

of molecular transitions

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

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para-tolualdehyde:Information Transfer Through Conjugated bonds?

V6 vs. V3 barrier to internal rotationWalther Caminati, Angela R. Hight-Walker, Jon T. Hougen, Isabelle Kleiner,

Hilkka Saal, Jens-Uwe Grabow, to be published.

Will the methyl group know about the asymmetry?

H

O

C1

3

2

1 2

3

1

2

3

Top view: Side view:along internal rotation axis

aldehyde group introduces asymmetry:

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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

Cl

H3H2

C3 axis

C3 E C3 C3²

E (123) (123)² = (132)

A1 1 1 1

E 1 *

1 *

H. C. Longuet-Higgins, Mol. Phys. 6 (1963), 445.J. T. Hougen, J. Chem. Phys. 37 (1962), 1433; J. Chem. Phys. 39 (1963), 358.

C3 group

H1

H2H3

H

O

C1

3

2

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tunnel-pathways, tunnel-Hamilton matrix,energy level split diagram K=0, vt=0

symmetric matrix, 2 eigenvalues:

W1= W(A1)=H11+2HE

W2=W3=W(E1)=H11-HE

Htunneling: rotation of CH3-group

H11

H11

H11

HE HE

HE

3 (feasible) equivalent

tunneling pathways in total:

H1

Cl

H3H2

C3 axis

H1

H2H3

Γ(G6)

J0J

E1

A1

2Htunneling

Htunneling

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V6/V3- torsional barrier

0 50 100 150 200 250 300 3500

5

10

15

20

25

30

V3=25.09 cm

-1, V

6= -5 cm

-1

V3=23.79 cm-1, V

6=+5 cm-1

V3=24.47 cm-1, V

6= 0 cm-1

En

ergy

(cm

-1)

Angle (degrees)

perfect fit to torsional groundstate (vt=0) spectrum archieved

for different contributions

to the barrier

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free internal rotor – high barrier torsion

m = 0

|m| = 1

|m| = 2

|m| = 3

|m| = 4

A

A

A

E

E

Evt = 2

vt = 1

vt = 0

E

V

0 ∞

gi = 2 gi = 3

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“free jet“ (FJ)absorption mm-wave setup

Side View

Top View

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

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

FJ-A-MMW COBRA-FT-MW

Jet Temperature

~20 K

~ 2 K

Sweep Rate 10 GHz/day 0.2 GHz/day

Relative Line Intensity

Nearly Boltzmanian

Altered

Resolution 0.2 MHz 3 kHz (10-7 cm-1)

Accuracy 0.050 MHz 0.3 kHz (10-8 cm-1)

Sensitivity 10-7 - 10-8 cm-1 10-10 - 10-12 cm-1

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para-tolualdehyde: J = 34 33 a R-band

T 50 K required broken diffusion pump heaters!

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0 60 120 180 240 300 3600

20

40

60

80

100

m=±3

m=±4

m=±2

m=±1

m=0

E,vt=2

A,vt=2

A,vt=1

E,vt=1

E,vt=0

A,vt=0

V3=24.5 cm

-1, V

6=0

Ene

rgy

(cm

-1)

Angle (degrees)

low-barrier torsional energy level diagram

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para-tolualdehyde:reduced energy level diagram for m = +/- 3

E – (1/2)(B+C)J(J+1)

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para-tolualdehyde:Information Transfer Through Conjugated bonds!

nlm CONSTANT OPERATOR VALUE STD DEV  202 A 0.166516196839980 0.000006112879081

B 0.032937322496368 0.000000063427868 C 0.027601452277977 0.000000064713936 DAB -0.002971620212815 0.000002362977471

211 RHORHO 0.030970392251857 0.000027764172184 220 F 5.490882492526767 0.003675124595046

V3 28.369747250217017 0.016741884821443 404 DJ 0.000000000766043 0.000000000002449

DJK -0.000000001773117 0.000000000020899 DK 0.000000040780968 0.000000002059929 ODELN 0.000000000152421 0.000000000001598 ODELK 0.000000002114823 0.000000000235953

413 ALV 0.000000004455893 0.000000000607588 AK1 0.000000241437257 0.000000041691112 ODELTA -0.000000067481273 0.000000015991851 C4 0.000000007123842 0.000000004163024

422 GV 0.000000119369360 0.000000034361650 AK2 0.000013649424323 0.000003574497292 DELTA -0.000009595953284 0.000001553935395 C1 0.000000455984320 0.000000016495752 FV -0.000009370236146 0.000000061416459 ODAB -0.000073087515674 0.000002201896216

431 AK3 0.000240896878198 0.000019336762283 440 V6 -5.328585545552866 0.025635841540561

AK4 -0.013457652989215 0.000793909144900 642 AMV -0.000000029064949 0.000000005471985

BK1 -0.000003052251718 0.000001041520361 C3 -0.000000161746243 0.000000005990665

DELTAB 0.000002198996436 0.000000272705423

result of global fit

to ~800 transitions in

5 different torsional states

at experimental accuracy

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para-tolualdehyde:Information Transfer Through Conjugated bonds!

barrier to internal rotation: V3 = 28.3 >> V6 = 5.3 cm-1

the methyl group does know about the orientation of thealdehyde group hiding in the plane - but not from sterical hindering!

H

O

C1

3

2

Top view: Side view:along internal rotation axis

1 2

3

1

2

3

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AcknowledgementAcknowledgement

Deutsche Forschungsgemeinschaft (DFG)

Land Niedersachsen

Deutscher Akademischer

Austauschdienst (DAAD)

Università di Bologna

Minister of Education, Italy