Spectroscopy with lasers

Demtröder, Wolfgang

doi:10.1007/3-540-06334-x_5

Cited by 7 publications

(2 citation statements)

References 436 publications

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“…Ref. 35,36,37). Two-dimensional (2D) coherent spectroscopy, which is one of the recent additions to this class of techniques, has enabled us to directly observe the coherent components of the excited-state dynamics3839.…”

Section: Resultsmentioning

confidence: 99%

Enhancement of Vibronic and Ground-State Vibrational Coherences in 2D Spectra of Photosynthetic Complexes

Chenu

Christensson

Kauffmann

et al. 2013

Sci Rep

166

188

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A vibronic-exciton model is applied to investigate the recently proposed mechanism of enhancement of coherent oscillations due to mixing of electronic and nuclear degrees of freedom. We study a dimer system to elucidate the role of resonance coupling, site energies, vibrational frequency and energy disorder in the enhancement of vibronic-exciton and ground-state vibrational coherences, and to identify regimes where this enhancement is significant. For a heterodimer representing two coupled bachteriochloropylls of the FMO complex, long-lived vibronic coherences are found to be generated only when the frequency of the mode is in the vicinity of the electronic energy difference. Although the vibronic-exciton coherences exhibit a larger initial amplitude compared to the ground-state vibrational coherences, we conclude that, due to the dephasing of the former, both type of coherences have a similar magnitude at longer population time.

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Section: Resultsmentioning

confidence: 99%

Enhancement of Vibronic and Ground-State Vibrational Coherences in 2D Spectra of Photosynthetic Complexes

Chenu

Christensson

Kauffmann

et al. 2013

Sci Rep

166

188

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“…Nine discrete wavelengths range from 5145A to 4545 A (or from 19430 cmr» to 21996 em- 1 ) can be individually selected. The laser light was focused into the sample cell by a 10 em focal length lens.…”

Section: Resultsmentioning

confidence: 99%

Resonance Fluorescence of Gaseous Chlorine Excited by Laser Light

Choe

Chang

Hwang

1977

J Chinese Chemical Soc

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A powerful argon ion laser was used to excite gaseous chlorine molecules resonantly from the X 1 ::E ground electronic state to the Aall excited electronic state. Three progressions of P; R doublets which correspond to the excitation from 1=37, 13 and 39 of v=O of the Xl~state to v'=22. 1'=38; v'=18, J'=12 and v'=16, JI=38 of the A'a state, respectively, and then decaying to various vibrational levels of the XI L state were observed. Of those, only the excitation from v=O, J=38 to v'=22. JI=38 transition has been reported before. Due to the extremely small transition probabilities, the spectral lines are much weaker than those of iodine and bromine. Their positions and their relative intensities were analyzed and compared with the result calculated from the known molecular constants and with the known Franck-Condon factors. Our data are consistent with the calculated results within the range of experimental error.The monochromatic radiation of a powerful laser is an ideal light source in the study of resonance fluorescence effect. Since 1967 many diatomic molecules, such as Nat, K I • Li l • BaO· and CUO,l} have been studied by this method. There are two advantages of using lasers in the fluorescence study: (1) Due to the strong intensity of the laser output, transitions with small transition probabilities and of low molecular concentrations can be studied; (2) Due to its monochromaticity, molecules are resonantly excited only to few excited states, therefore the spectra obtained are much simpler and easier to be analyzed than the spectra obtained from other excitation methods.The halogen gases are among the most interesting samples in laser fluorescence studies because not only they can be excited by light from the powerful argon ion laser, but also their transition probabilities are small. The fluorescence and the lifetime measurement of bromine and iodine gases excited by the argon ion laser light have been studied thoroughly.l.e) On the other hand, only one progression of four P, R doublets of respnance fluorescence lines of the chlorine gas has been observed using 4880A laser light excitation by Holzer, Murphy and Bernstein,» The reason is probably that, even excited .by strong laser light, the spectra of chlorine gas are still very weak. In fact, the transition probability between the Ala and the

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Neues Nachweisverfahren für nicht direkt faßbare Zwischenprodukte photochemischer Reaktionen

Kaupp¹,

Grüter²

1978

Angewandte Chemie

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lich ( I ), substituierte Tetrathiocane und elementaren Schwefel (sowieallerdings rnit geringerer Wirkungauch elementares Selen) so anzugreifen, daB sich bereits unter milden Bedingungen Copolymere rnit interessanten Eigenschaften bilden. So liefert z.B. ein aquimolares Gemisch von (1) und (2) bei ca. 100°C rnit BF3.Et20 in praktisch quantitativer Ausbeute ein Polymethylensulfid-Gemisch, das zwischen 245 und 265 "C unzersetzt schmilzt. Selbst bei einem Molverhaltnis von ( I ) zu (2) wie 4 : 1 entsteht das polymere Produkt (CHIS), noch rnit 87 % Ausbeute (allerdings wegen der hoheren Schmelztemperatur des Ausgangsgemisches erst bei ca. 150°C).Die oligomeren Thioformaldehyde bilden Silberkomplexe, die man zu ihrer Trennung benutzen k a n r~ [~] .Auch das gekornte Polymer aus der vorstehend beschriebenen Reaktion komplexiert Ag+-Ionen aus waoriger Losung. Durch waRriges NH3 werden diese Ionen unter Riickbildung des reinen Polymers wieder eluiert.Schon friiher haben wir (1) und (2) am Kohlenstoff in unterschiedlichem Grad substituiert (R= CH3, Si(CH3)3, Ge(CH3)3, Sn(CH3)3 oder COOH statt H)[31. Diese Derivate kiinnen, ebenso wie reines ( I ) , rnit (2) unter BF3-Katalyse copolymerisiert werden, wobei das urspriingliche Substitutionsmusterdem Verhaltnis der Reaktanden entsprechend modifiziertan den Kohlenstoffatomen der C-S-C-Ketten wieder zu finden ist.ErwartungsgemaR werden die Eigenschaften der neuen Polymere durch die Substituenten deutlich beeinflufit. Sie weisen in der Regel breite Schmelzbereiche auf und sind teilweise thermoplastisch. Enthalten sie Carboxygruppen, so eignen sie sich als Ionenaustauscher (die Ionenselektivitat muR noch untersucht werden).Aus oligomeren Thioformaldehyden und elementarem Schwefel sind homogene Schmelzen erhaltlich, deren physikalische Eigenschaften von denen des reinen Schwefels stark abweichen. LaBt man ein geschmolzenes Gemisch von (2) und S8 rnit BF3.Etz0 reagieren, wird ein betrachtlicher Teil des Schwefels in das unlosliche polymere Produkt eingebaut. Auch dabei sollte sich zunachst das reaktive Zwischenprodukt (3) bilden, das dann im zweiten Schritt die Schwefelringe offnet: Arbeitsvorschrijien (typische Beispiele) a) 1.84g (0.01 mol) (2) werden rnit 1.38g (0.01 mol) (1) vermischt und geschmolzen. Gibt man zur klaren, homogenen Schmelze bei ca. 100°C ein Tropfchen BF3.Et20, so wird sie innerhalb weniger Sekunden fest. Das sprode Polymerisat wird mechanisch zerkleinert und 8 h rnit Benzol extrahiert, wobei 0.13g (1) in Losung gehen. Ausbeute an (CHIS),: 3.09 g (96 %). Das praktisch farblose Produkt schmilzt klar zwischen 260 und 265°C; wenig dariiber zersetzt sich die Schmelze langsam unter Gasentwicklung. b) 1.84g (0.01 mol) (2) und 2.28g (0.01 mol) 1,3,5,7-Tetra-thiocar1-2-carbonsaure[~~~ werden rnit 10 ml Xylol aufgeschllmmt und zum Sieden erhitzt. Nach Zusatz eines Tropfchens BF3.Et20 wird abgesaugt, der feste Riickstand mehrmals rnit heiRem Benzol, dann rnit konzentrierter NH3-Losung und schlienlich rnit verdiinnter Salzsaure gewaschen. Das getrocknete, farblose, feink...

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Spectroscopy with lasers

Cited by 7 publications

References 436 publications

Enhancement of Vibronic and Ground-State Vibrational Coherences in 2D Spectra of Photosynthetic Complexes

Enhancement of Vibronic and Ground-State Vibrational Coherences in 2D Spectra of Photosynthetic Complexes

Resonance Fluorescence of Gaseous Chlorine Excited by Laser Light

Neues Nachweisverfahren für nicht direkt faßbare Zwischenprodukte photochemischer Reaktionen

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