Strong-field phase-dependent molecular dissociation

Nichols, Sarah R.; Weinacht, Thomas; Rozgonyi, Tamás; Pearson, Brett J.

doi:10.1103/physreva.79.043407

Cited by 27 publications

(58 citation statements)

References 19 publications

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“…The normal mode vibrational coordinate of the parent cation in its ground electronic state was also determined with the same method. As pointed out in previous publications [25,26], strong field ionization of CH 2 BrI by a near infrared (IR) ∼30 fs laser pulse induces a vibrational wave packet in the I-C-Br bending mode in the ground electronic state of CH 2 BrI + . With a simple one-dimensional model we were able to describe the time-dependent formation of CH 2 Br + by a probe pulse as the wave packet oscillates on the ground ionic state surface and comes into resonance with higher lying dissociative states [26].…”

Section: Calculationsmentioning

confidence: 82%

“…5. As discussed in [25], modulations in the various ion yields versus time delay can be interpreted as ionization to V 1 by the pump followed by transfer to V 3,4 (where the molecule dissociates and which is the dominant contribution) by the probe as the wave packet crosses FC 2 during evolution on V 1 . The evolution of the wave packet on V 1 can be described theoretically as one-dimensional motion along the bending coordinate [26].…”

Section: B Pump-probe Parametrizationmentioning

confidence: 99%

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Pulse-shape-dependent strong-field ionization viewed with velocity-map imaging

et al. 2011

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We explore strong field molecular ionization with velocity map imaging of fragment ions produced by dissociation following ionization. Our measurements and ab initio electronic structure calculations allow us to identify various electronic states of the molecular cation populated during ionization, with multiple pathways to individual states highlighted by the pulse shape dependence. In addition, we show that relative populations can be reconstructed from our measurements. The results illustrate how strong field molecular ionization can be complicated by the presence and interaction of multiple cationic states during ionization.

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Section: Calculationsmentioning

confidence: 82%

Section: B Pump-probe Parametrizationmentioning

confidence: 99%

Pulse-shape-dependent strong-field ionization viewed with velocity-map imaging

et al. 2011

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“…Dihalomethanes have been utilized in cyclopropanation reactions of alkenes due to their unique photochemistry in solution. [3][4][5][6][7][8][9] The potential for optical control [10][11][12][13][14][15][16] arises from the manifold of electronic states involved 17 and the rapid photochemistry that is competitive with internal deactivation and redistribution of the incident energy. 18,19 In general, UV absorption in dihalomethanes promotes an electron from a nonbonding halogen orbital (n X ) into a halogen-carbon antibonding orbital (σ * C-X ), causing cleavage of the carbon halogen bond.…”

Section: Introductionmentioning

confidence: 99%

Solvent dependent branching between C-I and C-Br bond cleavage following 266 nm excitation of CH2BrI

Anderson

Spears

Wilson

et al. 2013

The Journal of Chemical Physics

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It is well known that ultraviolet photoexcitation of halomethanes results in halogen-carbon bond cleavage. Each halogen-carbon bond has a dominant ultraviolet (UV) absorption that promotes an electron from a nonbonding halogen orbital (nX) to a carbon-halogen antibonding orbital (σ*C-X). UV absorption into specific transitions in the gas phase results primarily in selective cleavage of the corresponding carbon-halogen bond. In the present work, broadband ultrafast UV-visible transient absorption studies of CH2BrI reveal a more complex photochemistry in solution. Transient absorption spectra are reported spanning the range from 275 nm to 750 nm and 300 fs to 3 ns following excitation of CH2BrI at 266 nm in acetonitrile, 2-butanol, and cyclohexane. Channels involving formation of CH2Br + I radical pairs, iso-CH2Br-I, and iso-CH2I-Br are identified. The solvent environment has a significant influence on the branching ratios, and on the formation and stability of iso-CH2Br-I. Both iso-CH2Br-I and iso-CH2I-Br are observed in cyclohexane with a ratio of ~2.8:1. In acetonitrile this ratio is 7:1 or larger. The observation of formation of iso-CH2I-Br photoproduct as well as iso-CH2Br-I following 266 nm excitation is a novel result that suggests complexity in the dissociation mechanism. We also report a solvent and concentration dependent lifetime of iso-CH2Br-I. At low concentrations the lifetime is >4 ns in acetonitrile, 1.9 ns in 2-butanol and ~1.4 ns in cyclohexane. These lifetimes decrease with higher initial concentrations of CH2BrI. The concentration dependence highlights the role that intermolecular interactions can play in the quenching of unstable isomers of dihalomethanes.

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“…Also for these results no physical mechanism was reported to explain these results. Weinacht and co-workers [32][33][34] have recently reported several papers on the strong-field wave-packet driven dissociation and concerted elimination in CH 2 I 2 and ionic fragmentation in CH 2 BrI and CH 2 ClI. These experiments were carried out with 800 nm pulses with pulse intensities of 1-2ϫ 10 14 Watt/ cm 2 .…”

Section: Previous Chirp Experiments Using Lif or Tof-mass Detectionmentioning

confidence: 99%

“…More recently, the group of Weinacht has reported several studies using pump-probe spectroscopy to study wavepacket dynamics and control in halomethanes. [32][33][34] From these multiphoton excitation studies at 800 nm, Weinacht and coworkers conclude that resonances between ionic surfaces of the parent ion facilitate the formation of ionic fragments.…”

Section: Introductionmentioning

confidence: 99%

Toward elucidating the mechanism of femtosecond pulse shaping control in photodynamics of molecules by velocity map photoelectron and ion imaging

Irimia

Janssen

2010

The Journal of Chemical Physics

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High-resolution threshold photoelectron study of the propargyl radical by the vacuum ultraviolet laser velocitymap imaging method J. Chem. Phys. 135, 224304 (2011) Competitive ionization processes of anthracene excited with a femtosecond pulse in the multi-photon ionization regime J. Chem. Phys. 135, 214310 (2011) Interaction of nanosecond laser pulse with tetramethyl silane (Si(CH3)4) clusters: Generation of multiply charged silicon and carbon ions AIP Advances 1, 042164 (2011) Photoelectron spectroscopy of the molecular anions, Li3O and Na3O J. Chem. Phys. 135, 164308 (2011) Interpretation of the photoelectron spectra of superalkali species: Li3O and Li3O J. Chem. Phys. 135, 164307 (2011) Additional information on J. Chem. Phys. The control of photofragmentation and ionization in a polyatomic molecule has been studied by femtosecond chirped laser pulse excitation and velocity map photoelectron and ion imaging. The experiments aimed at controlling and investigating the photodynamics in CH 2 BrCl using tunable chirped femtosecond pulses in the visible wavelength region 509-540 nm at maximum intensities of about 4 ϫ 10 13 W / cm 2 . We observe that the time-of-flight mass spectra as well as the photoelectron images can be strongly modified by manipulating the chirp parameter of ultrashort laser pulses. Specifically, a strong enhancement of the CH 2 Cl + / CH 2 BrCl + ion ratio by a factor of five and changes in the photoelectron spectra are observed for positively chirped pulses centered near 520 nm. These changes are only observed within a narrow window of wavelengths around 520 nm and only for positively chirped pulses. From the combination of the photoelectron spectra and the ion recoil energy of the CH 2 Cl + fragment we can deduce that the parent ionization and fragmentation is induced by a multiphoton excitation with five photons. The photoelectron images and the fragment ion images also provide the anisotropy ͑␤-parameter͒ of the various electron bands and fragment ions. We conclude that multiphoton excitation of the highest occupied 22aЈ and 8aЉ CH 2 BrCl molecular orbitals of Br-character are both involved in the five-photon ionization, however, only excitation of the 22aЈ orbital appears to be ͑mostly͒ involved in the chirped control dynamics leading to enhanced fragmentation to CH 2 Cl + ͑X AЈ͒ +Br͑ 2 P 3/2 ͒. We propose that a wavepacket following or a time-delay resonance mechanism between the two-photon excited n x ͑Br, 22aЈ͒ → ͑2AЈ͒ repulsive surface and the three-photon near-resonant n x ͑Br, 22aЈ͒ → Rydberg͑AЈ͒ state of the neutral CH 2 BrCl molecule is responsible for the enhanced excitation of the n x ͑Br, 22aЈ͒ molecular orbital with up-chirped pulses. This leads to enhanced ionization to a configuration in the CH 2 BrCl + ͑X AЈ͒ continuum just above the dissociation limit of the CH 2 Cl + +Br͑ 2 P 3/2 ͒ channel, resulting in enhanced fragmentation.

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Strong-field phase-dependent molecular dissociation

Cited by 27 publications

References 19 publications

Pulse-shape-dependent strong-field ionization viewed with velocity-map imaging

Pulse-shape-dependent strong-field ionization viewed with velocity-map imaging

Solvent dependent branching between C-I and C-Br bond cleavage following 266 nm excitation of CH2BrI

Toward elucidating the mechanism of femtosecond pulse shaping control in photodynamics of molecules by velocity map photoelectron and ion imaging

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