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Ultraschnelle nichtlineare Raman-Messungen von Molekülen und Clustern

English title Structural and vibrational investigations of molecules and clusters by ultrafast nonlinear Raman techniques
Applicant Leutwyler Samuel
Number 144490
Funding scheme Project funding (Div. I-III)
Research institution Departement für Chemie und Biochemie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Physical Chemistry
Start/End 01.10.2012 - 31.08.2016
Approved amount 351'730.00
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Keywords (6)

degenerate four-wave mixing; coherent anti-Stokes Raman; supersonic beams; ultrafast spectroscopy; rotational coherence; Raman spectroscopy

Lay Summary (German)

Lead
Genaue Bestimmung von Molekülstrukturen
Lay summary

Ziel des Projekts ist die extrem genaue Bestimmung der Struktur von nicht-polaren Molekülen und Molekül-Dimeren. Chemische Bindungslängen und -winkel sind oft nur auf 0.1% genau bekannt, weil sie in mesit Kristallen gemessen werden, in welchen durch die Gitterkräfte die molekulare Struktur leicht deformiert wird. Andererseits sind molekulare Bindungslängen und Winkel in der Gasphase mit modernen theoretisch-chemischen Methoden heute auf besser als 0.01% genau berechenbar.

Im Rahmen des Vorläuferprojekts wurde eine ramanspektroskopische Methode entwickelt, die es erlaubt, die Strukturen von nicht-polaren Molekülen auf ca. 0.001 % genau (oder besser) zu messen. Mit dieser Genauigkeit wurden bisher die Strukturen symmetrischer Cycloalkane (Cyclopropan, Cyclobutan, Cyclopentan, Cyclohexan, Cycloheptan) und von Cycloalkenen (z.B. Benzol, Trifluorobenzol, Hexafluorobenzol, Cyclooctatetraen) bestimmt. Die Messdaten werden mit den Resultaten der aktuell besten theoretisch-chemischen Methoden verglichen.

Im Rahmen dieses Projekts sollen die Messungen ausgedehnt werden auf die Bestimmung der Strukturen von langkettigen Kohlenwasserstoffen wie z.B. n-Alkane (n-Butan, n-Pentan, n- Hexan usw.) oder n-Alkene (Butadien, Hexatrien, Octatetraen usw.).

Direct link to Lay Summary Last update: 29.04.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Accurate gas-phase structure of para -dioxane by fs Raman rotational coherence spectroscopy and ab initio calculations
Den Takuya, Menzi Samuel, Frey Hans-Martin, Leutwyler Samuel (2017), Accurate gas-phase structure of para -dioxane by fs Raman rotational coherence spectroscopy and ab initio calculations, in The Journal of Chemical Physics, 147(7), 074306-074306.
Probing the Structure, Pseudorotation, and Radial Vibrations of Cyclopentane by Femtosecond Rotational Raman Coherence Spectroscopy
Kowalewski P. Frey H. M. Infanger D. Leutwyler S. (2015), Probing the Structure, Pseudorotation, and Radial Vibrations of Cyclopentane by Femtosecond Rotational Raman Coherence Spectroscopy, in The Journal of Physical Chemistry A, 119(45), 11215-11225.
Rotational constants and structure of para-difluorobenzene determined by femtosecond Raman coherence spectroscopy: A new transient type
Den T. S. Frey H. M. Felker P. M. Leutwyler S. (2015), Rotational constants and structure of para-difluorobenzene determined by femtosecond Raman coherence spectroscopy: A new transient type, in The Journal of Chemical Physics, 143, 144306-1-144306-12.
Accurate rotational constant and bond lengths of hexafluorobenzene by femtosecond rotational Raman coherence spectroscopy and ab initio calculations
Den T. S. Frey H. M. Leutwyler S. (2014), Accurate rotational constant and bond lengths of hexafluorobenzene by femtosecond rotational Raman coherence spectroscopy and ab initio calculations, in The Journal of Chemical Physics, 141, 194303-1-194303-9.

Collaboration

Group / person Country
Types of collaboration
Prof. Peter Felker, University of California at Los Angeles, Los Angeles United States of America (North America)
- Publication
Prof. Thomas Feurer, Institut für angewandte Physik, Universität Bern, Bern Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Prof. Dr. John Stanton, Dept. of Chemistry and Biochemistry, University of Texas at Austin, Austin United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results

Associated projects

Number Title Start Funding scheme
119932 Ultraschnelle nichtlineare Raman-Messungen von Molekülen und Clustern 01.04.2008 Project funding (Div. I-III)
152816 Spektroskopie, Photophysik und Photochemie von Molekülclustern in Überschallmolekularstrahlen 01.04.2014 Project funding (Div. I-III)
130376 Ultraschnelle nichtlineare Raman-Messungen von Molekülen und Clustern 01.04.2010 Project funding (Div. I-III)

Abstract

High resolution rotational spectroscopy of nonpolar molecules in gas cells and cooled in supersonic jet expansions will be performed by femtosecond (fs) rotational Raman coherence spectroscopy (RCS), detected by degenerate four-wave mixing (DFWM). The main goal is the determination of accurate rotational and centrifugal distortion constants of nonpolar molecules of fundamental chemical interest. For lack of a dipole moment, nonpolar molecules cannot absorb radiation in the microwave to millimeter-wave range and cannot by studied by usual rotational spectroscopic methods. In fs rotational Raman methods, a set of stimulated rotational Raman transitions of the sample is excited by two coincident polarized laser pulses that are much shorter (80 fs) than the characteristic rotational period of the molecules (typically several 100 ps). This initiates a rotational wavepacket in the sample that is probed in a sensitive and background-free way by a third probe pulse via a degenerate four-wave mixing process. This allows to determine highly accurate molecular geometries (bond distances and angles) of nonpolar molecules that are not otherwise accessible. We plan to study the following nonpolar molecules:- n-alkanes (e.g., n-butane to n-decane),- trans-alkenes (e.g., butadiene, hexatriene, octatetraene),- larger cycloalkanes (cycloheptane, cyclooctane, cyclononane, cyclodecane)- nonpolar bicycloalkanes (e.g., decalin, [2.2.2]bicyclooctane)- nonpolar aromatics, organometallicsAlso planned are the further development and efficiency improvements of the computer programs employed for the fitting of molecular parameters to the RCS transients of symmetric and asymmetric tops (e.g. genetic algorithm fitting, use of fast Fourier transform methods).
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