Ultrafast photodissociation dynamics of electronically excited CF2I2 molecules

Radloff, W.; Farmanara, P.; Stert, V.; Schreiber, E.; Huber, J. Robert

doi:10.1016/s0009-2614(98)00551-x

Cited by 38 publications

(37 citation statements)

References 11 publications

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“…Radloff et al reported an identical shift of the peak maxima in the CF 2 ϩ , I 2 ϩ , and the I ϩ transients. 18 We observed a shift of the peak maxima to longer times, indicating multiphoton contributions of the probe laser. A more detailed discussion of the contribution can be found below.…”

Section: A Transientsmentioning

confidence: 65%

Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Roeterdink

Janssen

2002

The Journal of Chemical Physics

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The femtosecond pump-probe technique is used in combination with velocity map ion imaging to study the photodissociation dynamics of CF 2 I 2 . Velocity map ion imaging provides the kinetic energy and the angular recoil distribution of the detected fragments. It enables us to distinguish between multiple photoexcitation and dissociation pathways leading to the same ionic fragment. For the dissociation of CF 2 I 2 with delayed femtosecond pulses at 264 and 396 nm, various ionic fragments and dissociation channels are observed. Especially interesting dynamics is observed for the molecular detachment of I 2 . It is found that at short pump-probe delay ͑р250 fs͒ I 2 ϩ can be formed via a one-photon excitation at 264 nm and subsequent ionization of the dissociating neutral CF 2 I 2 molecule. This excitation pathway produces slow I 2 ϩ fragments recoiling predominantly parallel along the polarization of the 264 nm pump laser. At long delay time ͑у500 fs͒ this pathway is closed and the formation of molecular I 2 ϩ proceeds via a two-photon excitation at 264 nm to a highly electronically excited state of the CF 2 I 2 molecule. The molecular detachment of I 2 is via a concerted asynchronous dissociation producing a highly internally excited I 2 * fragment, possibly in the 2 ⌸ 3/2 5d;2g state. The highly excited I 2 fragments are ionized by a single 396 nm photon producing I 2 ϩ fragments. The kinetic energy of this pathway is higher and the I 2 ϩ fragments are recoiling perpendicular with respect to the polarization of the pump laser.

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Section: A Transientsmentioning

confidence: 65%

Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Roeterdink

Janssen

2002

The Journal of Chemical Physics

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“…It has been well established that ultraviolet excitation of CH 2 I 2 in both gas and solution phases results in direct cleavage of the C-I bond to produce CH 2 I radical and I atom fragments [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][77][78][79] and this indicates that step 1 in the above reaction mechanism is the primary photochemical start of the reaction. It has been clearly experimentally demonstrated that some of the initially produced CH 2 I radical and I atom fragments can undergo solvent-induced geminate recombination to form a CH 2 I-I isomer species within a few picoseconds 79,88 and this establishes that step 2 of the proposed reaction mechanism occurs to an appreciable extent in room-temperature solutions.…”

Section: And Solvation Of the Hi Leaving Groupmentioning

confidence: 99%

“…Gas-phase ultraviolet photolysis of polyhalomethanes generally leads to one direct carbon-halogen bond cleavage. [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] Time-of-flight photofragment spectroscopy results indicate that the polyatomic photofragment typically receives a large amount of excitation of its internal degrees of freedom ͑vibration and rotation͒. 44,[47][48][49][50][51] Gas-and solutionphase resonance Raman experiments for several polyhalomethanes showed that photodissociation typically had a noticeable multidimensional character and Franck-Condon region dynamics qualitatively consistent with a semirigid radical description of the dissociation process.…”

Section: Introductionmentioning

confidence: 99%

Efficient dehalogenation of polyhalomethanes and production of strong acids in aqueous environments: Water-catalyzed O–H-insertion and HI-elimination reactions of isodiiodomethane (CH2I–I) with water

Kwok

Zhao

Guan

et al. 2004

The Journal of Chemical Physics

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A combined experimental and theoretical study of the ultraviolet photolysis of CH2I2 in water is reported. Ultraviolet photolysis of low concentrations of CH2I2 in water was experimentally observed to lead to almost complete conversion into CH2(OH)2 and 2HI products. Picosecond time-resolved resonance Raman spectroscopy experiments in mixed water/acetonitrile solvents (25%-75% water) showed that appreciable amounts of isodiiodomethane (CH2I-I) were formed within several picoseconds and the decay of the CH2I-I species became substantially shorter with increasing water concentration, suggesting that CH2I-I may be reacting with water. Ab initio calculations demonstrate the CH2I-I species is able to react readily with water via a water-catalyzed O--H-insertion and HI-elimination reaction followed by its CH2I(OH) product undergoing a further water-catalyzed HI-elimination reaction to make a H2C=O product. These HI-elimination reactions produce the two HI leaving groups observed experimentally and the H2C=O product further reacts with water to produce the other final CH2(OH)2 product observed in the photochemistry experiments. These results suggest that CH2I-I is the species that reacts with water to produce the CH2(OH)2 and 2HI products seen in the photochemistry experiments. The present study demonstrates that ultraviolet photolysis of CH2I2 at low concentration leads to efficient dehalogenation and release of multiple strong acid (HI) leaving groups. Some possible ramifications for the decomposition of polyhalomethanes and halomethanols in aqueous environments as well as the photochemistry of polyhalomethanes in the natural environment are briefly discussed.

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“…[10][11][12][13][14][15][16][17] The gas-phase findings following photoexcitation of CF 2 I 2 with different excitation wavelengths (λ) are summarized in Scheme 1. [10][11][12][13][14][15][16][17] We have recently reported the formation of molecular iodine in 32% quantum yield following 350 nm excitation of CF 2 I 2 in n-hexane. 18 This result was surprising, as the gas-phase formation of molecular iodine following the excitation of CF 2 I 2 requires at least a 193 nm photon.…”

Section: Introductionmentioning

confidence: 99%

Structure of the Photochemical Reaction Path Populated via Promotion of CF₂I₂ into Its First Excited State

et al. 2009

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The photochemical reaction path following the promotion of CF(2)I(2) into its lowest-lying excited electronic singlet state has been modeled using ab initio multiconfigurational quantum chemical calculations. It is found that a conical intersection drives the electronically excited CF(2)I(2)* species either to the CF(2)I + I radical pair or back to the starting CF(2)I(2) structure. The structures of the computed relaxation pathways explain the photoproduct selectivity previously observed in the gas phase. Furthermore, the results provide the basis for explaining the condensed-phase photochemistry of CF(2)I(2).

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Ultrafast photodissociation dynamics of electronically excited CF2I2 molecules

Cited by 38 publications

References 11 publications

Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Efficient dehalogenation of polyhalomethanes and production of strong acids in aqueous environments: Water-catalyzed O–H-insertion and HI-elimination reactions of isodiiodomethane (CH2I–I) with water

Structure of the Photochemical Reaction Path Populated via Promotion of CF₂I₂ into Its First Excited State

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Ultrafast photodissociation dynamics of electronically excited CF2I2 molecules

Cited by 38 publications

References 11 publications

Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Efficient dehalogenation of polyhalomethanes and production of strong acids in aqueous environments: Water-catalyzed O–H-insertion and HI-elimination reactions of isodiiodomethane (CH2I–I) with water

Structure of the Photochemical Reaction Path Populated via Promotion of CF2I2 into Its First Excited State

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Structure of the Photochemical Reaction Path Populated via Promotion of CF₂I₂ into Its First Excited State