Picosecond and nanosecond kinetic spectroscopic investigations of the relaxation and the solute—solvent reaction of electronically excited 3,5-dinitroanisole

Varma, Cyril A. G. O.; Plantenga, F.L.; Huizer, A. Herbert; Zwart, J.P.; Bergwerf, P.; Ploeg, J. P. M. van der

doi:10.1016/0047-2670(84)80059-3

“…Possible pathways include dissociation of the initially prepared state as well as internal conversion and/or intersystem crossing foUowed by dissociation from lower lying electronic surfaces, High internal conversion rates in nitro aromatic compounds have been attributed to strong vibronic coupling between the excited and ground electronic states due to the NO2 group. [ 11] The decomposition channels following UV excitation and rapid internal conversio_l should be similar to the channels found for thermal dissociation processes. In the studies presented here, the primary products for unimolecular decomposition of rfitrobenzene following 266 nm excitation were identified.…”

Section: Discussionmentioning

confidence: 70%

“…Since electronically excited molecules can relax via both radiative and nonradiative pathways, UV excitation is an alternative method of preparing highly vibrationally excited molecules in the ground electronic state. Many of the nitroaromatic ul compounds do not exhibit fluorescence or phosphorescence at'ter electronic , excitation [ 11], suggesting the excited singlet states relax predominantly through nonradiative channels. Possible pathways include dissociation of the initially prepared state as well as internal conversion and/or intersystem crossing foUowed by dissociation from lower lying electronic surfaces, High internal conversion rates in nitro aromatic compounds have been attributed to strong vibronic coupling between the excited and ground electronic states due to the NO2 group.…”

Section: Discussionmentioning

confidence: 99%

Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

Chu¹

1991

0

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Inelastic scattering of highly vibrationally excited molecules in the ground m electronic state was studied under single collision conditions using crossed molecular°b eams. The vibrational to translational (V-+T) energy transfel_ in collisions between 1 large highly vibrationally excited polyatomics and rare gases was havestigated by time-of-E flight +techniques. Two different methods, UV excitation followed by internal conversion + I and infrared multiphoton excitation ¢IIRMPE),were u_d to form vibrationaUy excited molecular beams of hexafluorobenzene and sulfur hexafluoride, respectively, The product translational energy was found to be independent of the vibrational excitation. + :These results indicate that the probability distribution function for V--,T energy transfer = is peaked at zero. The collisional relaxation of large polyatomic molecules with rare gases ,host likely occurs through a rotationally mediated process.. The photodissociation of nitrobenzene in a molecular beam was studied using the _ 266 nm radiation, Two primary dissociation channels were identified including simple --J bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy rad_c_. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Additionally., secondary, ,, .... , J dissociation c f the phenoxy radicals to carbon mo.oxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne.The development and characterization of a supersonic methyl radical beam source is described, The beam source configuration and conditions were optimized for CH3 production from the thermal decomposition o! azome'.hane. Elastic scatlering of methyl radical and neon was used to differentiate, between the methyl radicals and the residual azomethanc in the mol_.cular beam, This source was built in preparation for methyl radical photodissociation and re.active scattering studies.

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“…Recently, a pulsed CH3 supersonic beam source was used to study the resonant multiphoton spectrum of rotationally cold radicals. [11] In this nozzle design, the esthnated contact time in the heated region was .--100 _tsec.…”

Section: Discussionmentioning

confidence: 99%

“…where the mutual collision diameteris given by the collision diameters of the two gases _2ab (2'2)*is the collision integral which ffaa + Obb with themselves by gab-2 . [11] includes parameters to describe the interaction potential and Nb is the concentration.…”

Section: The Master Equationmentioning

confidence: 99%

Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

Chu

¹

1991

0

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Inelastic scattering of highly vibrationally excited molecules in the ground m electronic state was studied under single collision conditions using crossed molecular°b eams. The vibrational to translational (V-+T) energy transfel_ in collisions between J bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy rad_c_. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Additionally., secondary, ,, .... , J dissociation c f the phenoxy radicals to carbon mo.oxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne. The development and characterization of a supersonic methyl radical beam source is described, The beam source configuration and conditions were optimized for CH3 production from the thermal decomposition o! azome'.hane. Elastic scatlering of methyl radical and neon was used to differentiate, between the methyl radicals and the residual azomethanc in the mol_.cular beam, This source was built in preparation for methyl radical photodissociation and re.active scattering studies.

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“…13,14 This mechanism of photoreduction is especially efficient for electron-donor substituted nitroaromatics since in these cases the low energy excited states are of the π-π* type. 15 These types of excited states tend to form hydrogen bonds in the nitro group side, [16][17][18] and the corresponding radical anions are rather basic (the pK a value in water for the protonated radical anion of p-nitrophenol is 3.6, significantly higher than other nitroaromatics, for instance the value for protonated p-dinitrobenzene is 1.6). 19 Generally all these process coexist, making the outcome of the photoreactions complex, and reducing their synthetic usefulness.…”

Section: Introductionmentioning

confidence: 99%

Electrostatic effects on the photoreactions of nitrophenyl ethers with nucleophiles

Marquet¹,

Tomasi²

2003

Arkivoc

1

0

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Nucleophilic aromatic photosubstitutions of 1,2-dialkoxy-4-nitrobenzenes by oxygen nucleophiles such as water or alcohols in basic media and in air equilibrated solutions, lead to low yields of substitution, following the "polar" S N Ar * mechanism. Photoreduction of the nitro group is the exclusive process in an inert atmosphere. By using Topologically Controlled Coulombic Interactions (TCCI), the photosubstitution process becomes predominant, allowing the SET mechanism for S N Ar * reactions to occur. This is due, on one hand, to the reduced tendency of the radical anion to be oxidized, and on the other hand, to the removal of electronic density from the nitro group in the radial anion which lowers the rate of proton transfer from the nucleophile radical cation.

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Picosecond and nanosecond kinetic spectroscopic investigations of the relaxation and the solute—solvent reaction of electronically excited 3,5-dinitroanisole

Cited by 29 publications

References 71 publications

Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

Electrostatic effects on the photoreactions of nitrophenyl ethers with nucleophiles

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