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Spectroscopic Characterization of Radicals by Degenerate and Two-Color Resonant Four-Wave Mixing

English title Spectroscopic Characterization of Radicals by Degenerate and Two-Color Resonant Four-Wave Mixing
Applicant Radi Peter
Number 124542
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Physical Chemistry
Start/End 01.01.2010 - 31.12.2012
Approved amount 163'815.00
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Keywords (8)

Radicals; Combustion; Four-wave mixing; Discharge; Molecular beam; High-resolution spectroscopy; Nonlinear spectroscopy; Perturbations

Lay Summary (English)

Lead
Lay summary
Thermodynamic data are indispensable for combustion modeling. In many combustion systems the temperature range spans from 300 to 2300 K and therefore enthalpy, entropy and heat capacity data for each species is required for a large temperature range. This proposal describes spectroscopic experiments on combustion relevant radical species that are required to determine thermodynamic functions via the partition function and statistical mechanical relationships. In contrast to stable molecules, direct measurements of thermodynamic properties of radicals are generally impossible due to the high reactivity and transient character of these open-shell molecules.For the intended work, measurements are based (i) on the carefully optimized production of specific, internally cold radicals in the controlled environment of a molecular beam and (ii) on the application of highly sensitive and selective non-linear four-wave mixing (FWM) spectroscopy. By taking into account the sensitivity and selectivity of FWM spectroscopy of transient species from the slit-jet discharge source, we suggest further experiments on important radicals for combustion. The ethynyl, vinyl and peroxy radicals are targeted for initial experiments. However, numerous important radicals are present in the beam and the characterization of the source might lead to different, more favored (combustion relevant) molecules for beginning investigations.The rotationally resolved single and double-resonance spectra, in combination with other spectroscopic methods, will provide important information on the principal moment of inertia, rotational constants, perturbations, symmetry number and vibrational frequencies of low-lying electronic levels. In fact, apart from the FWM techniques, more conventional methods, like laser-induced fluorescence (LIF), cavity ring-down (CRD), multi-photon ionization with ns and fs-lasers are available in the laboratory. Furthermore, complementary experiments at the VUV beam line of the SLS, which is operated by members of this group, are envisaged The spectroscopic data from the proposed experiments are important to assess thermodynamic function experimentally. These values are essential for combustion modeling and provides means to benchmark the demanding calculations of these open shell species.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Polarization- and time-resolved DFWM spectroscopy of the A 2Σ+ - X 2Π (0,0) band transitions of nascent OH radicals generated by 266 nm laser photolysis of H2O2
Maksyutenko Pavlo, Radi P.P., Kozlov Dimitrii, Kouzov Alexander (2013), Polarization- and time-resolved DFWM spectroscopy of the A 2Σ+ - X 2Π (0,0) band transitions of nascent OH radicals generated by 266 nm laser photolysis of H2O2, in Journal of Raman Spectroscopy, 44(10), 1349-1355.
Re-visiting the observation of the Δv = - 4 vibronic sequence of the C2 Swan system
Bornhauser P, Sych Y, Knopp G, Gerber T, Radi PP (2013), Re-visiting the observation of the Δv = - 4 vibronic sequence of the C2 Swan system, in Chemical Physics Letters, 572, 16-20.
Shedding light on a dark state: The energetically lowest quintet state of C[sub 2]
Bornhauser P., Sych Y., Knopp G., Gerber T., Radi P. P. (2011), Shedding light on a dark state: The energetically lowest quintet state of C[sub 2], in The Journal of Chemical Physics, 134(4), 044302-044302.
Degenerate and two-color resonant four-wave mixing of C2- in a molecular beam environment
Tulej Marek, Knopp Gregor, Gerber Thomas, Radi Peter P. (2010), Degenerate and two-color resonant four-wave mixing of C2- in a molecular beam environment, in Journal of Raman Spectroscopy, 41(8), 853-858.
Deperturbation study of the {d3[Pi]g,v'=4d3[Pi]g},v'=4 state of C2 by applying degenerate and two-color resonant four-wave mixing
Bornhauser P., Knopp G., Gerber T., Radi {P.P.} (2010), Deperturbation study of the {d3[Pi]g,v'=4d3[Pi]g},v'=4 state of C2 by applying degenerate and two-color resonant four-wave mixing, in Journal of Molecular Spectroscopy, 262(2), 69-74.
Direct absorption transitions to highly excited polyads 8, 10, and 12 of methane
Sadovskii D., Kozlov D., Radi P. (2010), Direct absorption transitions to highly excited polyads 8, 10, and 12 of methane, in Physical Review A, 82(1), 012503-1-012503-17.
Rotationally Resolved Ground State Vibrational Levels of {HC2S} Studied by {Two-Color} Resonant {Four-Wave} Mixing†
Chauhan Richa, Mazzotti Fabio J., Raghunandan Ranjini, Tulej Marek, Radi Peter P., Maier John P. (2010), Rotationally Resolved Ground State Vibrational Levels of {HC2S} Studied by {Two-Color} Resonant {Four-Wave} Mixing†, in The Journal of Physical Chemistry A, 114(9), 3329-3333.
Laser-induced grating spectroscopy of highly excited overtone and combination vibrational states of methane
Kozlov DN, Sadovskii DA, Radi PP, Laser-induced grating spectroscopy of highly excited overtone and combination vibrational states of methane, in Journal of Molecular Spectroscopy.

Collaboration

Group / person Country
Types of collaboration
F. Merkt, ETHZ Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Prof. R. Marquardt, Université de Strasbourg, France France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
D. Kozlov, A.M. Prokhorov General Physics Institute, Moscow Russia (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
John P. Maier, Universität Basel Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
D.A. Sadovskii, Université du Littoral Côte d'Opale, Dunkerque France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Seminar Individual talk High resolution spectroscopy of radicals in the gas phase by applying four-wave mixing techniques 23.10.2012 University of Lund, Sweden, Sweden Radi Peter;
European conference on non-linear optical spectroscopy ECONOS 2012 Talk given at a conference Two-color four-wave mixing spectroscopy: a tool to study angular momentum anisotropy 08.07.2012 aberdeen, UK, Great Britain and Northern Ireland Sych Yaroslav; Radi Peter;
High Resolution Molecular Spectroscopy (HighRus-2012) Talk given at a conference Perturbation assisted optical-optical double resonance spectroscopy of radical species by four-wave mixing techniques 02.07.2012 St. Petersburg, Russia, Russia Radi Peter;
tulip 2012, modern developments in spectroscopy Poster Two-color four-wave mixing spectroscopy: a tool to study angular momentum anisotropy 10.04.2012 NOORDWIJK, THE NETHERLANDS, Netherlands Sych Yaroslav;
Symposium on Femtosecond Filamentation and Standoff Laser Sensing, Vienna, Austria Talk given at a conference High resolution spectroscopy of radicals in the gas phase by applying four-wave mixing techniques 28.03.2012 Vienna, Austria, Austria Radi Peter;
31st Int. Symposium on Free Radicals, Port Douglas, Australia Poster Deperturbation studies of radicals by applying two-color resonant four-wave mixing 24.07.2011 Port Douglas, Australien, Australia Radi Peter;
European Conference on Nonlinear Optical Spectroscopy Talk given at a conference Intersystem crossing in radicals by two-color four-wave mixing 23.05.2011 Twente, Holland, Netherlands Sych Yaroslav; Radi Peter;


Associated projects

Number Title Start Funding scheme
146387 Spectroscopic Characterization of Radicals by Degenerate and Two-Color Resonant Four-Wave Mixing 01.04.2013 Project funding (Div. I-III)
115958 Characterization of Vibrationally and Rotationally Excited Molecules by Two-Color Resonant Four-Wave Mixing 01.04.2007 Project funding (Div. I-III)
175490 Mapping the electronic structure of transition metal dimers by degenerate and two-color four-wave mixing 01.10.2017 Project funding (Div. I-III)
115958 Characterization of Vibrationally and Rotationally Excited Molecules by Two-Color Resonant Four-Wave Mixing 01.04.2007 Project funding (Div. I-III)

Abstract

Thermodynamic data are indispensable for combustion modelling. In many combustion systems the temperature range spans from 300 to 2300 K and therefore, enthalpy, entropy and heat capacity data for each species is requred for a large temperature range. This proposal describes spectroscopic experiments on combustion relevant radical species that are required to determine thermodynamic functions via the partition function and statistical mechanical relationships. In contrast to stable molecules, direct measurements of thermodynamic properties of radicals are generally impossible due to the high reactivity and transient character of these open-shell molecules.For the intended work, measurements are based (i) on the carefully optimized production of specific, internally cold radicals in the controlled environment of a molecular beam and (ii) on the application of highly sensitive and selective non-linear four-wave mixing (FWM) spectroscopy. We outline the recent improvement of the radical production optimized for for the proposed investigations. A precursor diluted in a seed gas is discharged through a long and narrow slit into the vacuum apparatus and generates a two-dimensional expansion that is optimally suited for the FWM setup used in the experiment. The assembly yields a signal improvement over the previous cylindrical discharge of approximately two orders of magnitude. By taking advantage of the ultrafast laser system in our laboratory, the valve and discharge optimization for a specific precursor is achieved by applying fs-ionization mass spectrometry providing an essentially fragmentation free mass spectrum of the neutral radicals present in the beam. An example is shown for an acetylene/CS2 mixture diluted in argon producing numerous hydrocarbon radicals relevant to combustion.Our expertise and recent improvements of the sensitivity of FWM spectroscopy resulted in several publications on the transient species, C2, C3 and HC4S. Moreover, we have been able to detect C2-, the first anion observed by FWM to the best of our knowledge. Anions are typically by two orders of magnitude less abundant in the beam than their corresponding neutrals. In addition, we show that extremely weak satellite and perturbing transitions in the Swan system of C2 can be detected. The double resonance feature of the method provides means to measure spin-orbit constants more accurately and to perform deperturbation studies. Such measurements have not been possible by using linear one-photon measurements due to the complex spectrum that consist of many overlapping transitions.By taking into account the sensitivity and selectivity of FWM spectroscopy of transient species from the slit-jet discharge source, we suggest further experiments on important radicals for combustion. The ethynyl, vinyl and peroxy radicals are elaborated in more detail and show the problems that are typically encountered for the spectroscopic studies of small radicals. These molecules are targeted for initial experiments. However, numerous important radicals are present in the beam and the characterization of the source might lead to different, more favored (combustion relevant) molecules for beginning investigations.The rotationally resolved single and double-resonance spectra, in combination with other spectroscopic methods, will provide important information on the principal moment of inertia, rotational constants, symmetry number and vibrational frequencies of low-lying electronic levels. In fact, apart from the FWM techniques, more conventional methods, like laser-induced fluorescence (LIF), cavity ring-down (CRD), multi-photon ionization with ns and fs-lasers are available in the laboratory. Furthermore, complementary experiments at the VUV beam line of the SLS, which is operated by members of this group, are evisaged The spectroscopic data from the proposed experiments are important to assess thermodynamic function experimentally. These values are essential for combustion modeling and provides means to benchmark the demanding ab initio calculations of these open shell species.
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