Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Roeterdink, Wim G.; Janssen, Maurice H. M.

doi:10.1063/1.1505026

Cited by 15 publications

(14 citation statements)

References 27 publications

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“…30 The formation of molecular iodine is observed only upon excitation of CF 2 I 2 at 193 nm ͑6.5 eV͒. [33][34][35][36] In contrast to the gas-phase photochemistry, excitation of CF 2 I 2 in n-hexane with a single 350 nm photon ͑3.54 eV͒ leads to the ultrafast formation of molecular iodine in a 32% quantum yield. 37 Despite the fact that resonance Raman spectra of CF 2 I 2 are strongly solvent dependent, 38,39 the several picosecond build up of I 2 was observed in a wide range of solvents ͑methanol, acetonitrile, linear alkanes, and chlorinated alkanes͒.…”

Section: Introductionmentioning

confidence: 99%

Characterization of iso-CF2I2 in frequency and ultrafast time domains

El‐Khoury

George

Kalume

et al. 2010

The Journal of Chemical Physics

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The photolysis of diiododifluoromethane (CF(2)I(2)) in condensed phases was studied by a combination of matrix isolation and ultrafast time-resolved spectroscopy, in concert with ab initio calculations. Photolysis at wavelengths of 355 or 266 nm of CF(2)I(2):Ar samples (1:5000) held at approximately 8 K yielded iso-CF(2)I(2) (F(2)C-I-I), a metastable isomer of CF(2)I(2), characterized here for the first time. The infrared (IR) spectra of this isomer were recorded in matrix experiments, and the derived positions of the C-F stretching modes are in very good agreement with the predictions of high level ab initio calculations, which show that the iso-form is a minimum on the CF(2)I(2) ground state potential energy surface. The formation of this isomer following 350 nm excitation of CF(2)I(2) in room temperature CCl(4) solutions was monitored through its intense C-F stretching mode by means of ultrafast time-resolved IR absorption. Together, matrix isolation and ultrafast IR absorption experiments suggest that the formation of iso-CF(2)I(2) occurs via recombination of CF(2)I radical and I atom. Ultrafast IR experiments detect a delayed rise of iso-CF(2)I-I absorption, placing an upper limit of 400 fs for the C-I bond dissociation and primary geminate recombination processes. The product absorption spectrum recorded 1 ns after 350 nm excitation of CF(2)I(2) in solution is virtually identical to the visible absorption spectrum of iso-CF(2)I(2) trapped in matrix isolation experiments [with subtracted I(2)(X) absorption]. The formation of this isomer in solution at room temperature has direct dynamic implications for the ultrafast production of molecular iodine from electronically excited CF(2)I(2).

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Section: Introductionmentioning

confidence: 99%

Characterization of iso-CF2I2 in frequency and ultrafast time domains

El‐Khoury

George

Kalume

et al. 2010

The Journal of Chemical Physics

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“…13,15 During the last decade our first generation homebuilt cantilever piezo valve has been operating very reliably at a 1-kHz repetition rate and various molecular systems have been investigated using femtosecond velocity map imaging. 14,15,17,18 Recently, other groups have reported the implementation of the cantilever piezo valve, using the report by Gerlich and coworkers, for generating pulsed molecular beams at 1 kHz in femtosecond ion imaging experiments as well. 19 In our laboratory 20,21 the recent implementation of femtosecond photoelectron-photoion coincidence imaging experiments running at a repetition rate of the femtosecond regen system of 5 kHz has created a demand for a pulsed valve operating at 5 kHz.…”

Section: Introductionmentioning

confidence: 99%

In situ characterization of a cold and short pulsed molecular beam by femtosecond ion imaging

Irimia

Kortekaas

Janssen

2009

Phys. Chem. Chem. Phys.

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In this paper we report on the in situ characterization of the cold velocity distribution of a pulsed molecular beam produced by a novel cantilever piezo valve. The velocity distribution is measured at various temporal positions within the pulsed expansion using femtosecond velocity map ion imaging. It is shown that the universal detection of molecules by multi-photon femtosecond velocity map ion imaging can provide directly the velocity distribution with excellent velocity resolution. The novel cantilever piezo valve can operate both in continuous (DC) and pulsed mode without any modification using the same drive electronics. Pulsed operation was tested at repetition rates of 20 Hz, 1 kHz and 5 kHz and a conical nozzle 200 mum in diameter. The cantilever valve produces a pulsed molecular beam of translationally cold molecules at modest backing pressures of about 6 bar. At low to medium repetition rates (20-1000 Hz) the pulsed piezo valve produces pulses of 12-40 mus duration of translationally cold seeded beams of helium and neon with speed ratios up to S = 135 (20 Hz, 0.1% CD(3)I in neon) and S = 55 (1 kHz). At the highest tested repetition rate of 5 kHz, the speed ratio obtained for the same seeded beam is reduced to about S = 45. This is still more than a factor of two better than the speed ratio S = 21 measured for a continuous beam produced with the same nozzle at 0.5 bar backing pressure. The cold velocity distribution of the pulsed beam expansion as compared to a continuous beam expansion is beneficial for improved spatial resolution in velocity map ion imaging experiments at high repetition rates of 1-5 kHz. The cantilever piezo valve has a simple design and may find broad applicability in areas where short gas pulses are warranted because of limited pumping speed, the effective use of (expensive) samples or the production of translationally and internally cold molecular beams at high repetition rate. When operating the piezo valve at high backing pressures of 15-30 bar extensive clustering of the low percentage (0.1-0.5%) seeded molecules in He and Ne carrier gasses can be produced of interest for cluster research.

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“…This is in agreement with previous studies for this [6] and similar molecules. [7,8] Fragment ions can be generated either by dissociation of the parent ion, or by ionization after dissociation along neutral channels. Both fragment ion (CH 3 + and I + ) signals show enhancement for long delays between the pump and probe pulses, although of much lower intensity than that of near temporal overlap.…”

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confidence: 99%

Femtosecond Transition‐State Imaging of the A‐Band CH₃I Photodissociation

et al. 2008

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Since the early days of femtosecond transition state spectroscopy, both the clocking of the reaction (on-resonance experiments) and the detection of transient species along the reaction coordinate (off-resonance experiments) have been at the heart of femtochemistry. [1][2][3] In the pioneering experiments carried out by Zewail and co-workers, the real time photodissociation of ICN was studied by tuning the probe laser on-resonance to the first electronic excited state of the CN fragment which then emits fluorescence.[4] The resonant probe laser opens up an optical coupling region on the potential energy surface (determined by its bandwidth), which allows the clocking of the reaction from the initial Franck-Condon wave packet to the free fragments in the asymptotic region. However, the beauty of femtochemistry arises from the detection of the transient species between the initial and asymptotic wave packets by tuning the probe laser off-resonance to the free fragment.The introduction of femtosecond time-resolved kinetic energy time-of-flight (KETOF) by Zhong and Zewail [5] showed the possibility of observing the dynamics of transition states and final products at the same time, using one wavelength for the probe and only resolving the kinetic energy. By following the time evolution of the kinetic energy of the fragment ion, the dissociation dynamics from the initial transition state to the final products could be studied and several examples, in particular the A-band photodissociation of CH 3 I, were presented. Using this method, the evolution of the kinetic-energy-resolved cations is followed by accessing ionic surfaces to study the dissociation dynamics of neutral molecules. Only one probe laser is used to detect the transition states and final products.Herein, we combine off-resonance multiphoton ionization for the probing step using a femtosecond laser pulse at 800 nm and velocity map imaging for ion detection to follow the time evolution of transition states and final products in the A-band photodissociation dynamics of CH 3 I at 266 nm. Photodissociation of CH 3 I in the near UV proceeds via excitation in the A-band, a broad featureless absorption continuum (220-350 nm) involving three optically allowed transitions from the ground state: two weak perpendicular transitions to the Ion signals corresponding to the parent ion CH 3 I + and the fragments CH 3 + and I + are measured from the oscilloscope trace as a function of the time delay between the 266 nm (pump) and the 800 nm (probe) pulses. We observe that all three ions are produced separately by each of the laser pulses, but we work under intensity conditions where such signals are minimized. When the delay time between the pump and the probe pulses is small, a strongly enhanced ion signal, lasting approximately 300 fs, is measured for the parent and all the fragments. When the probe pulse is fired later, the fragment ions show a weak, enhanced signal lasting longer than 100 ps, whereas the parent ion signal does not show any measurable enhancement. This b...

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Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Cited by 15 publications

References 27 publications

Characterization of iso-CF2I2 in frequency and ultrafast time domains

Characterization of iso-CF2I2 in frequency and ultrafast time domains

In situ characterization of a cold and short pulsed molecular beam by femtosecond ion imaging

Femtosecond Transition‐State Imaging of the A‐Band CH₃I Photodissociation

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Femtosecond velocity map imaging of concerted photodynamics in CF2I2

Cited by 15 publications

References 27 publications

Characterization of iso-CF2I2 in frequency and ultrafast time domains

Characterization of iso-CF2I2 in frequency and ultrafast time domains

In situ characterization of a cold and short pulsed molecular beam by femtosecond ion imaging

Femtosecond Transition‐State Imaging of the A‐Band CH3I Photodissociation

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Femtosecond Transition‐State Imaging of the A‐Band CH₃I Photodissociation