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Georg-August-Universitaet GoettingenTobias N. WassermannInstitute of Physical

ChemistryGoettingen

19/06/2006 61st Ohio State University Symposium on Molecular Spectroscopy

Proton tunneling estimates for malonaldehyde vibrations

from supersonic jet and matrix quenching experiments

Tobias N. Wassermann, Martin A. SuhmInstitute of physical chemistry, University of Goettingen, Tammannstr. 6, D-37077 Goettingen, Germany

David LuckhausChemistry Departement, University of British Columbia, 6174 University Blvd., Vancouver, BC, Canada

Stéphane CoussanLab. Physique des Interactions Ioniques et Moléculaires, UMR 6633, University of Marseille, Centre

St-Jérôme, 13397 Marseille Cedex 20, France

219/06/2006 Proton tunneling estimates for malonaldehyde vibrations

Tobias N. WassermannInstitute of Physical

ChemistryGoettingen

61st Ohio State University Symposium on Molecular Spectroscopy

Outline

Introduction Experimental setup Method of evaluation of the tunneling

splittings Comparison with acetylacetone Spectra and results Summary, conclusions Acknowledgement



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Malonaldehyde

• Stable in the enol form• two equivalent CS –structures• double minimum potential• tunneling splitting between the two wells



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Tunneling splitting in the ground state is known with high accuracyE0= 21.58 cm-1 [1]

Changes of splittings in vibrationally excited states are difficult to measureOnly two known examples:14= 512 cm-1: (E)≈ -6 cm-1 [2]

6= 1594 cm-1: (E)= -0.03 cm-1 [3]

[1]: S. L. Baughcum, Z. Smith, E. B. Wilson, R. W. Duerst, J. Am. Chem. Soc., 106(8), 2260, 1984D. W. Firth, K. Beyer, M. A. Dvorak, S. W. Reeve, A. Grushow, K. R. Leopold, J. Chem. Phys., 94(3), 1812, 1991

T. Baba, T. Tanaka, I. Morino, K. M. T. Yamada, K. Tanaka, J. Chem. Phys., 110(9), 4131, 1999[2]: C. J. Seliskar, R. E. Hoffman, J. Mol. Spectrosc., 96, 146, 1982[3]: C. Duan, D. Luckhaus, Chem. Phys. Lett., 391, 129, 2004



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T. D. Sewell, Y. Guo,D. L. Thompson,

J. Chem. Phys.,103(19), 8557, 1995

semiclassical

V. A. Benderskii, E. V. Vetoshkin,I. S. Irgibaeva, H.-P. Trommsdorff,

Russ. Chem. Bull, Int. Ed.,50(7), 1148, 2001

instanton trajectory

D. Tew, N. C. Handy, S. Carter,S. Irle J. Bowman,

Molec. Phys., 102(21-22),2217, 2004

quantum state calculations

R. Meyer, T.K. Ha,Molec. Phys.,

101(22), 3263, 2003

quantum state calculations



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Experimental Setup

Filet-Jet:Fine but lengthy600 x 0.2 mm

6 magnetic valves

High throughputMA does not formH-bonded clusters



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Carrier Gases

Helium• like free molecules in the gas phase at low temperatures

Argon• lower expansion-temperature• higher polarizability• may condense on the molecules

Amorphousflying Ar-Nano-matricesSpectracomparable withcrystalline matrix



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Rotational temperatures in the jet: 20 – 60 K.

Boltzmann distribution

~ 1 2



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Molecular symmetry group G4

if … is not seen in the spectra any splitting in spectra indicates

a vibrational dependence of thetunneling splitting

C. J. Seliskar, R. E. Hoffman, J. Mol. Spectrosc., 96, 146, 1982



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A side glance …Acetylacetone

R. Srinivasan, J. S. Feenstra, S. T. Park, S. Xu, A. H. Zewail,

J. Am. Chem. Soc., 126, 2266, 2004

Tunneling splitting not detected!

W. Caminati, J.-U. Grabow,J. Am. Chem. Soc., 128(3), 854,Jan. 2006

CS



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Ar-matrix,AcAc/Ar=2/1000

N2-matrix,AcAc/N2=4/1000

Jet He



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N2-matrix,AcAc/N2=4/1000

Ar-matrix,AcAc/Ar=2/1000

Jet He

Jet N2

Jet Ar

Only small matrix shifts in Acetylacetone (≤ 3 cm-1) Conclusion: any major matrix shifts in Malonaldehyde are caused

by quenching of the tunneling motion



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Quenching of the tunneling in a matrix

Direct Proton transfer: no longer a symmetrical double minimum

Symmetrical tunneling path: includes transfer of the heavy Ar atom



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CH at 767 cm-1:one band that shiftsby only about 1 cm-1

vibration does notaffect proton transfer

out of planeC-H bending mode



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OH out of plane O-H bending

• Jet: E1= 4.1 cm-1

• Matrix Comparison: E1= 4.8 cm-1

• Tunneling temperature: 10 – 20 K



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CO at 1594 cm-1:symmetric combination ofC=C/C=O stretching with OHin plane bending

from hi-res. spectroscopy:(E)= - 0.03 cm-1 C. Duan, D. Luckhaus, Chem. Phys. Lett., 391, 129, 2004

this work:He jet – Ar jet:(E)= - 1.4 cm-1 He jet – Ar matrix:(E)= - 3.2 cm-1

Error: 3 cm-1

tunnel splittingswith ± 6 cm-1

≈ 0 cm-1



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OH in plane OH bending, CH bending, CC stretching

• Jet: E1= 9.9 cm-1

• Matrix Comparison: E1= 8.2 cm-1



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Summary and Conclusions

New results for tunneling splittings of malonaldehyde vibrations have been obtained

Comparison of gas phase, jet and matrix spectra leads to excited state splittings

Accuracy is limited by the resolution or by other matrix influences than quenching

OH-bending reduces tunneling splitting

Evaluation of theoretical models

Starting points for hi-res. spectroscopy

* C. Duan, D. Luckhaus, Chem. Phys. Lett., 391, 129, 2004

T. N. Wassermann, D. Luckhaus, S. Coussan, M. A. Suhm,Phys. Chem. Chem. Phys. 2006, 8, 2344-2348 (Communication)



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T. D. Sewell, Y. Guo,D. L. Thompson,

J. Chem. Phys.,103(19), 8557, 1995

V. A. Benderskii, E. V. Vetoshkin,I. S. Irgibaeva, H.-P. Trommsdorff,

Russ. Chem. Bull, Int. Ed.,50(7), 1148, 2001

D. Tew, N. C. Handy, S. Carter,S. Irle J. Bowman,

Molec. Phys., 102(21-22),2217, 2004

R. Meyer, T.K. Ha,Molec. Phys.,

101(22), 3263, 2003

C. J. Seliskar, R. E. Hoffman, J. Mol. Spectrosc., 96, 146, 1982

C. Duan, D. Luckhaus,Chem. Phys. Lett.,

391, 129, 2004

This work


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Acknowledgement

Prof. Dr. M. Suhm Dr. D. Luckhaus C. Rice Dr. S. Coussan and his group from Université de Provence, Marseille Members of the Suhm group

Financial Support: GRK 782 of the DFG (www.pcgg.de)


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Thank youfor your

attention!


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Appendix



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AcAc C2v MA AcAc CS



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