Results 1 - 10 of 10
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[en] We perform an experimental investigation on tunneling ionization of CH_3X (X=I, Br, Cl) molecules in intense femtosecond laser fields (10"1"3 to 10"1"5 W/cm"2). The angular distribution of the parent and fragment ions from the well aligned molecular targets has been measured. Compared with theoretical calculation, the results show some new insights into the ionization mechanism of these molecules in intense laser fields. (paper)
[en] The resonant enhanced multiphoton ionization (REMPI) of OCS molecules has been studied by tracing the electron energy shift with the laser intensity dependent photoelectron energy spectra. We find that two excited states (1Δ and 1Π) have been involved in the ionization of OCS at 800 nm and the REMPI through a certain excited state can be selectively controlled by varying the laser intensity. Furthermore, the REMPI of OCS through 4sσ Rydberg states at 400 nm laser fields has also been identified by angular distribution of electrons. (paper)
[en] We report experimental results on strong-field laser interact with aligned CH_3CI molecules, the ejection of fragments H_n"+ dependent on alignment of CH_3Cl molecules has been studied. The mechanism of fragmentation builds on the alignment sensitive ionization and dissociation from inner and outer valence orbitals or the excitation process of molecular have been discussed. (paper)
[en] Photoelectron images from single ionization of OCS molecules are measured at 800 nm or 400 nm linearly polarized laser pulses (∼50 fs) using velocity-map imaging techniques. The resonant ionization of the molecules has been studied by tracing the electron energy shift in the photoelectron energy spectra at different laser intensities, and the contributions of three excited states at certain laser intensities and wavelengths are identified. During the ionization of OCS molecules, two excited states (1Δ and 1∏) are shifted into resonance at different 800 nm laser intensities, and the Rydberg state 4 pσ ∏ is involved in the resonance for a 400 nm laser. The demonstration of resonant excitation contribution experimentally will help further the understanding of OCS ionization in strong laser fields. (paper)
[en] We study the molecular orbital dependent tunneling ionization and quantum interference during laser-driven rescattering electron wavepacket of O2 by performing the channel-resolved photoion and photoelectron measurements. The shifted above threshold ionization electron spectra demonstrate that direct ionization of HOMO-2 to the excited cation state contributes significantly to the generation of fragment ions, while the parent ions are generated from tunneling ionization of highest occupied molecular orbital (HOMO). Furthermore, the destructive and constructive interferences between different rescattering orbits from strong-field ionization of HOMO and HOMO-2 are confirmed by the measured channel and angle-resolved photoelectron momentum distribution. (paper)
[en] Photoionization/photodissociation of cyclopentanone is performed by using a time-of-flight mass spectrometer (TOF-MS) with synchrotron vacuum ultraviolet radiation (105-140 nm). The photoionization mass spectrum and photoionization efficiency (PIE) curves of fragment ions are measured. the appearance potentials (AP) of these ions are obtained from their PIE curves. Energies of neutrals and cations of parent and its fragments have been calculated using Gaussian03 program with the G3 method. From these data, the dissociation energies of the dissociation channels have been evaluated. Comparing the theoretical and experimental results the possible channels of cyclopentanone have been analyzed. (authors)
[en] We studied the relative yields and dissociation dynamics for two- and three-body Coulomb explosion (CE) channels from highly charged carbonyl sulfide molecules in intense laser fields using the CE imaging technique. The electron recollision contributions are evaluated by comparing the relative yields for the multiple ionization process in linearly polarized and circularly polarized (LP and CP) laser fields. The nonsequential multiple ionization is only confirmed for the charge states of 2 to 4 because the energy for further ionization from the inner orbital is much larger than the maximum recollision energy, 3.2U p. The novel deviations of kinetic energy releases distributions between LP and CP pulses are observed for the charge states higher than 4. It can be attributed to the stronger molecular bending in highly charged states before three-body CE with CP light, in which the bending wave packet is initialed by the triple or quartic ionization and spread along their potential curves. Compared to LP light, CP light ionizes a larger fraction of bending molecules in the polarization plane. (paper)
[en] In this paper, k step chaometry (k SCM) is defined based on monopolized sphere and instantaneous chaometry (ICM), and the convergent theorem of asymptotical periodic orbit is also proved. The 400 SCM of the discrete model of Lorenz system is calculated and results disclose that 400 SCM can clearly identify the parameters of chaotic dynamic system. The EEG instrument is applied to measure time series of EEG, and it is observed that the instantaneous chaometry of the EEG and the data generated from Lorenz attractor produce similar results.
[en] The concepts of uniform index and expectation uniform index are two mathematical descriptions of the uniformity and the mean uniformity of a finite set in a polyhedron. The concepts of instantaneous chaometry (ICM) and k step chaometry (k SCM) are introduced in order to apply the method in statistics for studying the nonlinear difference equations. It is found that k step chaometry is an indirect estimation of the expectation uniform index. The simulation illustrate that the expectation uniform index for the Lorenz System is increasing linearly, but increasing nonlinearly for the Chen's System with parameter b. In other words, the orbits for each system become more and more uniform with parameter b increasing. Finally, a conjecture is also brought forward, which implies that chaos can be interpreted by its orbit's mean uniformity described by the expectation uniform index and indirectly estimated by k SCM. The k SCM of the heart rate showes the feeble and old process of the heart.
[en] Uniform index is a conception that can describe the uniformity of a finite point set in a polyhedron, and is closely related to chaos. In order to study uniform index, the concept of contained uniform index is defined, which is similar to uniform index and has good mathematical properties. In this paper, we prove the convergence of the contained uniform index, and develop the base of proving the convergence of uniform index.