117 research outputs found
Probing Time-Dependent Molecular Dipoles on the Attosecond Time Scale
Photoinduced molecular processes start with the interaction of the
instantaneous electric field of the incident light with the electronic degrees
of freedom. This early attosecond electronic motion impacts the fate of the
photoinduced reactions. We report the first observation of attosecond time
scale electron dynamics in a series of small- and medium-sized neutral
molecules (N2, CO2, and C2H4), monitoring time-dependent variations of the
parent molecular ion yield in the ionization by an attosecond pulse, and
thereby probing the time-dependent dipole induced by a moderately strong near-
infrared laser field. This approach can be generalized to other molecular
species and may be regarded as a first example of molecular attosecond Stark
spectroscopy
Ultrafast modulation of electronic structure by coherent phonon excitations
Femtosecond x-ray absorption spectroscopy with a laser-driven high-harmonic
source is used to map ultrafast changes of x-ray absorption by femtometer-
scale coherent phonon displacements. In LiBH4, displacements along an Ag
phonon mode at 10 THz are induced by impulsive Raman excitation and give rise
to oscillatory changes of x-ray absorption at the Li K edge. Electron density
maps from femtosecond x-ray diffraction data show that the electric field of
the pump pulse induces a charge transfer from the BH4â to neighboring Li+
ions, resulting in a differential Coulomb force that drives lattice vibrations
in this virtual transition state
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Observation of correlated electronic decay in expanding clusters triggered by near-infrared fields
When an excited atom is embedded into an environment, novel relaxation pathways can emerge that are absent for isolated atoms. A well-known example is interatomic Coulombic decay, where an excited atom relaxes by transferring its excess energy to another atom in the environment, leading to its ionization. Such processes have been observed in clusters ionized by extreme-ultraviolet and X-ray lasers. Here, we report on a correlated electronic decay process that occurs following nanoplasma formation and Rydberg atom generation in the ionization of clusters by intense, non-resonant infrared laser fields. Relaxation of the Rydberg states and transfer of the available electronic energy to adjacent electrons in Rydberg states or quasifree electrons in the expanding nanoplasma leaves a distinct signature in the electron kinetic energy spectrum. These so far unobserved electron-correlation-driven energy transfer processes may play a significant role in the response of any nano-scale system to intense laser light
Observation of correlated electronic decay in expanding clusters triggered by near-infrared fields
When an excited atom is embedded into an environment, novel relaxation
pathways can emerge that are absent for isolated atoms. A well-known example
is interatomic Coulombic decay, where an excited atom relaxes by transferring
its excess energy to another atom in the environment, leading to its
ionization. Such processes have been observed in clusters ionized by extreme-
ultraviolet and X-ray lasers. Here, we report on a correlated electronic decay
process that occurs following nanoplasma formation and Rydberg atom generation
in the ionization of clusters by intense, non-resonant infrared laser fields.
Relaxation of the Rydberg states and transfer of the available electronic
energy to adjacent electrons in Rydberg states or quasifree electrons in the
expanding nanoplasma leaves a distinct signature in the electron kinetic
energy spectrum. These so far unobserved electron-correlation-driven energy
transfer processes may play a significant role in the response of any nano-
scale system to intense laser light
Attosecond control in photoionization of hydrogen molecules
ABSTRACT: We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1s g and 2p u states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses
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XUV excitation followed by ultrafast non-adiabatic relaxation in PAH molecules as a femto-astrochemistry experiment
Highly excited molecular species are at play in the chemistry of interstellar media and are involved in the creation of radiation damage in a biological tissue. Recently developed ultrashort extreme ultraviolet light sources offer the high excitation energies and ultrafast time-resolution required for probing the dynamics of highly excited molecular states on femtosecond (fs) (1âfs=10â15s) and even attosecond (as) (1 as=10â18âs) timescales. Here we show that polycyclic aromatic hydrocarbons (PAHs) undergo ultrafast relaxation on a few tens of femtoseconds timescales, involving an interplay between the electronic and vibrational degrees of freedom. Our work reveals a general property of excited radical PAHs that can help to elucidate the assignment of diffuse interstellar absorption bands in astrochemistry, and provides a benchmark for the manner in which coupled electronic and nuclear dynamics determines reaction pathways in large molecules following extreme ultraviolet excitation
Attosecond control in photoionization of D2
ABSTRACT: We study the dissociative photoionization of D2 by an attosecond pulse train (APT) in the presence of a near-infrared (IR) field. Strong oscillations in the D+ kinetic energy release spectrum with a half period of the optical cycle of the infrared field are observed and attributed to interferences between ionization pathways involving different harmonic orders of the APT due to the IR-induced coupling between the 1s(sigma)g and 2p(sigma)u
ionization channels
Characterizing the multi-dimensional reaction dynamics of dihalomethanes using XUV-induced Coulomb explosion imaging
Site-selective probing of iodine 4d orbitals at 13.1Â nm was used to characterize the photolysis of CH2I2 and CH2BrI initiated at 202.5Â nm. Time-dependent fragment ion momenta were recorded using Coulomb explosion imaging mass spectrometry and used to determine the structural dynamics of the dissociating molecules. Correlations between these fragment momenta, as well as the onset times of electron transfer reactions between them, indicate that each molecule can undergo neutral three-body photolysis. For CH2I2, the structural evolution of the neutral molecule was simultaneously characterized along the C-I and I-C-I coordinates, demonstrating the sensitivity of these measurements to nuclear motion along multiple degrees of freedom
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