Spectroscopy and Photodynamics of Relatively Large Molecules

Kommandeur, Jan

doi:10.1002/9780470141199.ch5

Cited by 18 publications

(2 citation statements)

References 37 publications

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“…Building on this foundation, Tric and co-workers − extended the concepts to include short-pulse excitation with coherent sources and treated isolated molecules at low temperatures. This treatment is appropriate to modern experiments using lasers and molecular beams and is in common use, particularly as extended by Kommandeur to include the effects of the laser coherence width.…”

Section: Resultsmentioning

confidence: 99%

“…Under the conditions of strong coupling (vρ ≫ 1, where ρ is the density of states), a characteristic biexponential fluorescence decay is seen, as is classically demonstrated in pyrazine. 20 The faster component is the result of the dephasing of the initially pumped pure singlet state, while the longer component is the composite decay of the mixed eigenstates, which have been diluted by the coupled dark levels.…”

Section: See Belowmentioning

confidence: 99%

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Enhancement of Triplet Stability in Benzene by Substituents with Triple Bonds

Johnson

Sears

2013

J. Phys. Chem. A

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Excitation of phenylacetylene (PA) and benzonitrile to their lowest singlet states in a molecular beam has previously been shown to immediately (only during the 8 ns laser pulse) result in long-lived species with low ionization potentials (Hofstein, J.; Xu, H.; Sears, T.; Johnson, P.M. J. Phys. Chem. A 2008, 112, 1195-1201). Using the fragmentation of ions produced by photoionization at various times after initial excitation as a diagnostic for molecular geometry evolution, the long-lived species in phenylacetylene is shown to be a PA state (most likely a triplet) rather than an isomer. Delayed fluorescence and a delayed photoelectron signal indicative of S1 are also seen, indicating a singlet-triplet mixing process that is not quite in the statistical-coupling limit and is parallel to the long-lived species channel. Electronic structure calculations indicate that the lowest triplet state of phenylacetylene is nonplanar with the ethynyl group bent in a trans-configuration out of the plane of the ring. The substituent π-electrons are significantly conjugated into the ring, resulting in a tendency toward a quinoidal structure, which may be related to the unusual excited state stability. These molecules constitute the first members of a new class of excited state behaviors.

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Section: Resultsmentioning

confidence: 99%

Section: See Belowmentioning

confidence: 99%

Enhancement of Triplet Stability in Benzene by Substituents with Triple Bonds

Johnson

Sears

2013

J. Phys. Chem. A

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Photodynamics of Small Aliphatic Ketones in a Supersonic Jet Expansion

Haas

Zuckermann

1989

Israel Journal of Chemistry

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The photodynamics of acetone and some other simple aliphatic ketones in the mt* state are discussed in the light of recent results obtained in seeded supersonic beams. The Born-Oppenheimer approximation is used to describe the sequence of events beginning with light absorption and ending in molecular fragmentation. Intersystem crossing is shown to be an important process even for the isolated molecule. Its rate increases with the internal energy and may be related to the density of states in the triplet state. For all molecules studied so far, the results can be rationalized by assuming that dissociation takes place on the triplet surface, the SI surface being stable in the energy range pertinent to these experiments (up to 35,000 ern-I above the ground state). Fluorescence spectroscopy may be used also to detect small clusters. In the case of acetone, their presence is indicated by the decrease in the intensity of some spectral lines as a function of cooling efficiency. The results are used to estimate an upper limit for the van der Waals binding energies. posal in the fragments of dissociating molecules, including vector correlations. The first aspect has been extensively discussed, experimentally and theoretically, in the case of pyrazine.v" and also of carbonyl compounds, such as methylglyoxal and biacetyl,? propynal," butynal,? and acetaldehyde,'? which are more closely related to the topic of this paper. Dissociation dynamics were mostly studied for three-or four-atom molecules: ICN, 15 H 20,16 HONO,17 and H 202.18,19 Some larger molecules were also studied, notably methylnitrite" and tertbutyl nitrite."Both aspects were extensively studied in the case of formaldehyde, for which the energy disposal into the different fragments was carefully measured." In the case of formaldehyde, spectroscopic assignments are reasonably well established, and perturbations can be analyzed to yield interstate interactions. Since photochemistry often involves curve-crossing (in the Born-Oppenheimer approximation), this molecule appears at present to provide the best link between spectroscopic and dynamic (time-resolved) studies.

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Qualitative Theory of Radiationless Transitions

Medvedev¹,

Ошеров²

1995

Springer Series in Chemical Physics

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Spectroscopy and Photodynamics of Relatively Large Molecules

Cited by 18 publications

References 37 publications

Enhancement of Triplet Stability in Benzene by Substituents with Triple Bonds

Enhancement of Triplet Stability in Benzene by Substituents with Triple Bonds

Photodynamics of Small Aliphatic Ketones in a Supersonic Jet Expansion

Qualitative Theory of Radiationless Transitions

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