13 research outputs found
exploding clusters dynamics probed by XUV fluorescence
Clusters excited by intense laser pulses are a unique source of warm dense
matter, that has been the subject of intensive experimental studies. The
majority of those investigations concerns atomic clusters, whereas the
evolution of molecular clusters excited by intense laser pulses is less
explored. In this work we trace the dynamics of clusters
triggered by a few-cycle 1.45-m driving pulse through the detection of XUV
fluorescence induced by a delayed 800-nm ignition pulse. Striking differences
among fluorescence dynamics from different ionic species are observed
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Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation
High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20-26âeV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected
Time-resolved predissociation of the vibrationless level of the B state of CH3I
The predissociation dynamics of the vibrationless level of the first Rydberg
state 6s (B 2E) state of CH3I has been studied by femtosecond-resolved velocity
map imaging of both the CH3 and I photofragments. The kinetic energy
distributions of the two fragments have been recorded as a function of the
pump-probe delay, and as a function of excitation within the umbrella and
stretching vibrational modes of the CH3 fragment. These observations are made
by using (2+1) Resonant Enhanced MultiPhoton Ionization (REMPI) via the 3pz
2A2" state of CH3 to detect specific vibrational levels of CH3. The vibrational
branching fractions of the CH3 are recovered by using the individual
vibrationally state-selected CH3 distributions to fit the kinetic energy
distribution obtained by using nonresonant multiphoton ionization of either the
I or CH3 fragment. The angular distributions and rise times of the two
fragments differ significantly. These observations can be rationalized through
a consideration of the alignment of the CH3 fragment and the effect of this
alignment on its detection efficiency. Two extra dissociation channels are
detected: one associated with Rydberg states near 9.2 eV that were observed
previously in photoelectron studies, and one associated with photodissociation
of the parent cation around 15 eV.Comment: submitted Physical Chemistry Chemical Physics (2011
Explosionsgefahren beim Umgang mit Acetylenflaschen und -buendeln nach der Ausbreitung eines Acetylenzerfalls Abschlussbericht
SIGLEAvailable from TIB Hannover: F95B2355+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman
High-harmonic transient grating spectroscopy of NO2 electronic relaxation.
We study theoretically and experimentally the electronic relaxation of NO(2) molecules excited by absorption of one âŒ400 nm pump photon. Semiclassical simulations based on trajectory surface hopping calculations are performed. They predict fast oscillations of the electronic character around the intersection of the ground and first excited diabatic states. An experiment based on high-order harmonic transient grating spectroscopy reveals dynamics occurring on the same time scale. A systematic study of the detected transient is conducted to investigate the possible influence of the pump intensity, pump wavelength, and rotational temperature of the molecules. The quantitative agreement between measured and predicted dynamics shows that, in NO(2), high harmonic transient grating spectroscopy encodes vibrational dynamics underlying the electronic relaxation.MOLCOTUV and ITNICONIC contract