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(a) Calculated XPS spectra of the ground and two excited states of uracil. (b) Difference between the measured photoelectron spectra with and without ultraviolet excitation as a function of the delay
Source publication
The time resolved photoionization of C 1s in uracil following excitation of the neutral molecule by 260 nm pulses has been studied at LCLS.
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Citations
... Recently, femtosecond x-ray pulses have become available at large-scale facilities such as slicing synchrotron sources [20] and FELs [6], and several experiments have been proposed which aim to probe ultrafast molecular dynamics using time- resolved inner-shell electron spectroscopy. McFarland et al. [21] have reported time-resolved Auger electron spectroscopy experiments performed in UV photoexcited thymine molecules and a first attempt has been made recently at the Linear Coher- ent Light Source (LCLS) free-electron laser to observe changes to the carbon 1s photoelectron spectrum in UV-excited uracil [22]. However, to the best of our knowledge, no experiments have been reported that directly extract structural dynamics information using inner-shell photoelectrons as a probe. ...
Due to its element and site specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here, we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH3I) is investigated by ionization above the iodine 4d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal-field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules.
... In particular processes of dissociation and ionization are useful to study possible different molecular mechanisms caused by the 355 nm laser radiation. Most of the available experimental data by the interaction with electrons, photons from laser are in the range of 220290 nm[8][9], synchrotron light of energy from 6 to 22 eV[10]and 260nm[11]or multiple charged ions[4]. In the present study, the photodissociation and photoionization of uracil in the multiple photon absorption regimes were investigated at the wavelength of 355 nm and intensities of radiation in the range 10 8 to 10 9 W·cm –2. ...
We present the experimental results from ionization and dissociation by multiphoton absorption (MPI) of uracil and a mixture of uracil with Ar using a Reflectron time of flight spectrometer along with radiation from 355 nm at pulsed Nd:YAG laser . We focus on the light ions production. The MPI mass spectra show that the presence and intensity of the resulting ions depend on the density power of the laser. The resulting ions in the mass spectra are identified and found similar behavior in the case of H+ and C+ as when multiple charged ions are used. Different results were found in contrast with those, recently reported, when electrons or photons of other wavelength were used. The number of 355nm absorbed photons was calculated accordingly to Keldysh theory and similar results were fond using pure uracil or uracil-Ar mixture. Our results are compared with those obtained in other laboratories under different experimental conditions, some of them show only partial agreement and differences are discussed.
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The
basic
processes in molecules of biological interest induced by the absorption of VUV and soft X-rays
are reviewed. The study of excitation, ionisation and dissociation in the gas phase on the one hand provides detailed information on the electronic structure and geometry that determine the functioning of these molecules in macroscopic systems and, on the other hand, sheds light on the microscopic effects of radiation damage
in living cells.
The molecular ability to selectively and efficiently convert sunlight into other forms of energy like heat, bond change, or charge separation is truly remarkable. The decisive steps in these transformations often happen on a femtosecond timescale and require transitions among different electronic states that violate the Born-Oppenheimer approximation (BOA) [1]. Non-BOA transitions pose challenges to both theory and experiment. From a theoretical point of view, excited state dynamics and nonadiabatic transitions both are difficult problems [2, 3] (see Figure 1(a)). However, the theory on non-BOA dynamics has advanced significantly over the last two decades. Full dynamical simulations for molecules of the size of nucleobases have been possible for a couple of years [4, 5] and allow predictions of experimental observables like photoelectron energy [6] or ion yield [7–9]. The availability of these calculations for isolated molecules has spurred new experimental efforts to develop methods that are sufficiently different from all optical techniques. For determination of transient molecular structure, femtosecond X-ray diffraction [10, 11] and electron diffraction [12] have been implemented on optically excited molecules.
