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Untersuchung ultraschneller Moleküldynamiken in verbrennungsrelevanten Molekülen mit zeitaufgelösten nicht linearen Raman Messungen

English title Investigation of ultrafast molecular dynamics of combustion relevant species by time resolved non-linear Raman spectroscopy
Applicant Knopp Gregor
Number 115917
Funding scheme Project funding
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Physical Chemistry
Start/End 01.04.2007 - 31.07.2008
Approved amount 85'300.00
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Keywords (12)

time resolved coherent spectroscopy; ultrafast spectroscopy; four-wave mixing; coherent anti-Stokes Raman; molecular dynamics; formaldehyde; time resolved; four wave mixing; energy transfer; femtosecond; Raman; combustion

Lay Summary (English)

Lay summary
In many cases the understanding of combustion processes on the fundamental basis of elementary chemical reactions and their associated rates remains ambiguous and ‘non-invasive’ spectroscopic methods are the only tools for further elucidation. Time-resolved spectroscopy is often complementary to frequency domain techniques and offers additional insights into the structure and the dynamical behavior of the investigated molecules. Such methods show a high potential for performing spectroscopy of unresolved energy states within electronic or ro-vibronic manifolds. Many molecules, involved in hydrocarbon combustion processes absorb light in the UV spectral range. In the first part of this project we successfully demonstrated the feasibility of resonant UV-fs-FWM methods, such as ‘UV- coherent anti Stokes Raman [CARS] and transient grating [TG] spectroscopy, on the polyatomic formaldehyde molecule to investigate the ground and excited state dynamics of H2CO.
Though formaldehyde has some model character, it is an important intermediate in combustion, and still provides interesting and unknown dynamics concerning its dissociation after photo excitation. The H2CO decomposition complicates because of multiple reaction pathways involved.We aim to investigate the dissociation dynamics of formaldehyde by using time dependent resonant FWM methods to unveil such fundamental processes on a molecular level and time base.
The importance of formaldehyde in the influence of low temperature compression ignition was reported recently, increasing the demand to monitor this species in a pressurized environment. The main dissociation reaction channels switch from molecular at low to the radical channel at moderate pressures. Collisional energy transfer is suggested to be responsible for this pressure dependence. As fs-FWM is sensitive to collision induced energy transfer in an ensemble of molecules, we additionally aim to investigate the H2CO dynamics under moderate pressures including self and foreign gas collisions.
Further, the origin of the soot production is still not fully understood and of major importance to combustion research. In this context the investigations should be extended to larger molecules such as e.g 1,5-hexadiyne. Hereby fs-FWM spectroscopy is proposed for monitoring fast nuclear rearrangements of C6H6 species preliminary to the formation of the first benzene ring.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
103475 Untersuchung ultraschneller Moleküldynamiken in verbrennungsrelevanten Molekülen mit zeitaufgelösten nicht linearen Raman Messungen 01.08.2004 Project funding