Angle-resolved and internuclear-separation-resolved measurements of the ionization rate of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>B</mml:mi></mml:math>state of I<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>by strong laser fields

Time-resolved femtosecond x-ray diffraction patterns from laser-excited molecular iodine are used to create a movie of intramolecular motion with a temporal and spatial resolution of 30 fs and 0.3 A. This high fidelity is due to interference between the non-stationary excitation and the stationary initial charge distribution. The initial state is used as the local oscillator for heterodyne amplification of the excited charge distribution to retrieve real-space movies of atomic motion onÅngstrom and femtosecond scales. This x-ray interference has not been employed to image internal motion in molecules before. Coherent vibrational motion and dispersion, dissociation, and rotational dephasing are all clearly visible in the data, thereby demonstrating the stunning sensitivity of heterodyne methods.High brightness ultrafast hard x-ray free electron lasers (FELs) can perform time-resolved x-ray diffractive imaging. Recent demonstrations of time-resolved crystal diffraction or time-resolved non-periodic imaging illustrate the power of these sources to trackÅngstrom-scale motion [1,2]. These have spurred new insights in broad areas of science, but have not fully realized the potential of x-ray FELs to image molecules with simultaneous sub-Ångstrom and few-femtosecond resolution. Previous x-ray or electron scattering experiments have used correlations between simulations and data to extract femtosecond molecular dynamics information [3][4][5][6][7].Here we propose and demonstrate an imaging method that employs a universal but unappreciated feature of time-resolved hard x-ray scattering that dramatically improves reconstructed images of charge motion, and enables femtosecond and sub-Ångstrom x-ray movies. The method relies on the "pump-probe" protocol, where motion is initiated by a short "start" pulse, and then interrogated at a later time by a "probe" pulse. The pumped fraction is small, and the unexcited fraction is our heterodyne reference [8].

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“…Similar cusp-like features are predicted but have not been observed directly before [24,27]. See simulation in Supplemental Material [21].…”

supporting

confidence: 72%

“…The excitation is spread over several hundred cm −1 (∼ 40 meV) by thermal broadening of the initial state. The wave packet is high in the anharmonic portion of the B-state potential, and the bound motion in the B-state appears highly dispersed [24,27].…”

mentioning

confidence: 99%

Self-Referenced Coherent Diffraction X-Ray Movie of Ångstrom- and Femtosecond-Scale Atomic Motion

et al. 2016

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“…These degrees of freedom allow for the study of the dependence of ionization on angle and internuclear separation [3,4].…”

Section: Introductionmentioning

confidence: 99%

Single ionization of molecular iodine

et al. 2017

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We performed a study of the single ionization of iodine, I 2 over a range of wavelengths. Single ionization of I 2 is unexpectedly found to have a contribution from inner molecular orbitals involving the 5s electrons. The I + I + dissociation channel was recorded through velocity map imaging and the kinetic energy release of each channel was determined with 2D fitting of the images. Most of the measured kinetic energy data were inconsistent with ionization to the X, A, and B states of I + 2 , implying ionization from deeper orbitals. A pump-probe Fourier transform technique was used to look for modulation at the X and A state vibrational frequencies, to see if they were intermediate states in a two step process. X and A state modulation was only seen for kinetic energy releases below 0.2 eV consistent with dissociation through the B state. From these results and intensity, polarization, and wavelength dependent experiments we found no evidence of bond softening, electron rescattering or photon mediation through the X or A states to higher energy single ionization channels.

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“…Typically, R cr is about a factor of 2 larger than the equilibrium internuclear separation R e [6,8,13] [6] in correspondence with a first experimental finding of T cr ∼ 166 fs [14]. Experiments [15,16] have shown that iodine can be ionized up to I 2 13+ , but due to much shorter pulse durations of ∼30 fs employed there, all charge states were effectively formed at internuclear separations less than R cr .…”

Section: Introductionmentioning

confidence: 57%

“…In the intense laser field the ionization rate of I 2 strongly depends on the orientation of the molecular axis with respect to the polarization direction as proven by the angular anisotropy in fragment distributions [11,13] and supported by calculations based on a field ionization, Coulomb explosion model [9]. Calculations performed for aligned molecules [9] show that, under our NIR intensity conditions (1.6 × 10 14 W/cm 2 ), the ionization to the I 2 3+ state at R e can only be achieved in a fraction of molecules with their molecular axis oriented parallel to the electrical field vector.…”

Section: Experimental Results In View Of a Classical Field Ionizmentioning

confidence: 99%

Strong-field ionization of molecular iodine traced with XUV pulses from a free-electron laser

et al. 2012

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Ultrafast dynamics of a molecular wave packet created by a strong 120-fs near-infrared (800 nm) laser pulse in iodine has been probed by synchronized 13.4-nm, 35-fs extreme-ultraviolet pulses delivered by the free-electron laser facility in Hamburg, FLASH. The kinetic energy release of the multiply charged ionic fragments reveals three essential steps of strong-field-induced molecular fragmentation dynamics: (i) The creation of I 2 2+ and (I 2 2+ ) * molecular ions proceeds within (75 ± 15) fs full-width-at-half-maximum. (ii) With the onset of the I 2 2+ fragmentation the probability to lose a further electron within the same optical laser pulse rises with increasing I + -I + internuclear separation and reaches its maximum after ∼30 fs with respect to the pulse maximum.(iii) Charge separation into the I 2 2+ → I 2+ + I dissociative channel with an asymmetric charge distribution is completed after (121 ± 22) fs.

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Angle-resolved and internuclear-separation-resolved measurements of the ionization rate of theBstate of I2by strong laser fields

Cited by 13 publications

References 26 publications

Self-Referenced Coherent Diffraction X-Ray Movie of Ångstrom- and Femtosecond-Scale Atomic Motion

Self-Referenced Coherent Diffraction X-Ray Movie of Ångstrom- and Femtosecond-Scale Atomic Motion

Single ionization of molecular iodine

Strong-field ionization of molecular iodine traced with XUV pulses from a free-electron laser

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