Resonance Raman Scattering in Photodissociating Halomethanes

Duschek, Frank; Schmitt, Michael; Vogt, Patrick; Materny, Arnulf; Kiefer, W.

doi:10.1002/(sici)1097-4555(199706)28:6<445::aid-jrs126>3.3.co;2-w

Cited by 11 publications

(16 citation statements)

References 5 publications

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“…The initial direct C-I bond cleavage of diiodomethane in the gas and solution phases is consistent with A-band resonance Raman investigations of the Franck-Condon region dynamics. [43][44][45][46][47][48] The three femtosecond transient absorption studies [40][41][42] display similar behavior with a fast rise segment of a few hundred femtoseconds due to the initial C-I bond cleavage followed by a fast decay segment ͑usually ascribed to some geminate recombination͒ and then a slower rise component on the picosecond time scale. The interpretations offered for these femtosecond experiments varied a bit depending on their assignment of the species responsible for the transient absorption.…”

Section: B Discussion Of Possible Photochemical Mechanism"s… For Thementioning

confidence: 99%

Photoisomerization reaction of CH2BrI following A-band and B-band photoexcitation in the solution phase: Transient resonance Raman observation of the iso-CH2I–Br photoproduct

Zheng

Phillips

2000

The Journal of Chemical Physics

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We present nanosecond transient resonance Raman experiments that investigate the photoproduct species formed following A-band and B-band excitation of bromoiodomethane in room temperature cyclohexane solutions. Density functional theory calculations were also performed for several species that have been proposed as photoproducts for photodissociation of bromoiodomethane in the condensed phase. Comparison of the experimental resonance Raman spectra to density functional theory computational results and results for the closely related iso-CH 2 I-I and iso-CH 2 Br-Br species demonstrated that the iso-CH 2 I-Br species is mainly responsible for a transient absorption spectrum that appears after either A-band or B-band photoexcitation of bromoiodomethane in cyclohexane solution. This is in contrast to previous results for low temperature ͑12 K͒ solids where mainly the iso-CH 2 Br-I species was observed following A-band photoexcitation of bromoiodomethane. Further density functional theory computational results indicate that the iso-CH 2 I-Br species is noticeably more stable than the iso-CH 2 Br-I species by about 4.1 kcal/mol. This suggests that although both iso-CH 2 I-Br and iso-CH 2 Br-I species may be initially produced following ultraviolet excitation of bromoiodomethane in cyclohexane solution, only the more stable isomer has a sufficiently long lifetime to be observed in our nanosecond timescale transient resonance Raman experiments. We compare results for the bromoiodomethane ultraviolet photodissociation/photoisomerization reactions in the condensed phase to those of the closely related diiodomethane system and discuss a probable mechanism for the formation of the iso-bromoiodomethane species in the condensed phase.

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Section: B Discussion Of Possible Photochemical Mechanism"s… For Thementioning

confidence: 99%

Photoisomerization reaction of CH2BrI following A-band and B-band photoexcitation in the solution phase: Transient resonance Raman observation of the iso-CH2I–Br photoproduct

Zheng

Phillips

2000

The Journal of Chemical Physics

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“…They followed the geminate recombination reforming the parent molecule by measuring transient absorption at 620 nm. The initial dynamics that take place upon excitation of CH 2 I 2 have been studied by Duschek et al in the gas phase (108) and in solution by Kwok & Phillips using resonance Raman scattering between 342 and 369 nm (93,94), and by Sundström and coworkers using pump-probe spectroscopy (103). Their findings indicate the involvement of the I-C-I symmetric stretch, antisymmetric stretch, and bending vibrational modes.…”

Section: Bound-free Transitions: Concerted-elimination Chemical Reactmentioning

confidence: 99%

COHERENTNONLINEARSPECTROSCOPY: From Femtosecond Dynamics to Control

Dantus

2001

Annu. Rev. Phys. Chem.

118

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This review focuses on the study of the dynamics of isolated molecules and their control using coherent nonlinear spectroscopic methods. Emphasis is placed on topics such as bound-to-free excitation and the study of concerted elimination reactions, free-to-bound excitation and the study of bimolecular reactions, and bound-to-bound excitation and the study of intramolecular rovibrational dynamics and coherence relaxation. For each case the detailed time-resolved information reveals possible strategies to control the outcome. Experimental results are shown for each of the reactions discussed. The methods discussed include pump-probe and four-wave mixing processes such as transient grating and photon echo spectroscopy. Off-resonance transient-grating experiments are shown to be ideal for the study of ground state dynamics, molecular structure, and the molecular response to strong field excitation.

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“…Resonance Raman investigations showed several polyhalomethanes have multidimensional reaction coordinates and short-time dynamics qualitatively consistent with a semirigid radical impulsive model of the photodissociation in both the gas and solution phases. [29][30][31][32][33][34][35][36][37][38] Ultraviolet excitation, direct photoionization, and radiolysis of CH 2 I 2 in the solution phase all give rise to characteristic absorption bands ϳ385 nm ͑strong intensity͒ and ϳ570 nm ͑moderate intensity͒ [39][40][41][42][43][44][45] which have been attributed to several different possible photoproduct species such as trapped electrons, 39 the cation of diiodomethane (CH 2 I 2 ϩ ), 43,45 and the isomer of diiodomethane ͑iso-CH 2 I-I͒. 41,42 Several femtosecond transient absorption studies examined the photodissociation reaction of CH 2 I 2 in the solution phase [46][47][48] using probe wavelengths of 620 nm, 46 400 nm, 47 and 290-1220 nm ͑Ref.…”

Section: Introductionmentioning

confidence: 99%

Transient resonance Raman spectroscopy and density functional theory investigation of iso-polyhalomethanes containing bromine and/or iodine atoms

Zheng

Fang

Phillips

2000

The Journal of Chemical Physics

103

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We report additional transient resonance Raman spectra and density functional theory computations for the products formed following ultraviolet photoexcitation of solution phase polyhalomethanes containing bromine and/or iodine atoms. We show that the iso-polyhalomethane photoproduct is responsible for the intense transient absorption band observed in the 350-470 nm region after ultraviolet excitation of polyhalomethanes in the solution phase. We examine the trends and correlation in the density functional theory optimized geometry and intense electronic absorption transition in the 350-470 nm region for the iso-polyhalomethanes containing bromine and/or iodine atoms. We explore the chemical reactivity of the iso-polyhalomethane species using density functional theory computations for the reaction of iso-CH 2 Br-Br with ethylene as an example. Our results and comparison with experimental data in the literature indicate that the iso-polyhalomethane species is most likely the methylene transfer agent in the cyclopropanation reactions of olefins using ultraviolet photoexcitation of polyhalomethanes in the solution phase. We briefly discuss the possibility that the photochemistry and chemistry of the iso-polyhalomethanes may give significant release of reactive halogens to the atmosphere.

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Resonance Raman Scattering in Photodissociating Halomethanes

Cited by 11 publications

References 5 publications

Photoisomerization reaction of CH2BrI following A-band and B-band photoexcitation in the solution phase: Transient resonance Raman observation of the iso-CH2I–Br photoproduct

Photoisomerization reaction of CH2BrI following A-band and B-band photoexcitation in the solution phase: Transient resonance Raman observation of the iso-CH2I–Br photoproduct

COHERENTNONLINEARSPECTROSCOPY: From Femtosecond Dynamics to Control

Transient resonance Raman spectroscopy and density functional theory investigation of iso-polyhalomethanes containing bromine and/or iodine atoms

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