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Light–matter interactions are usually described within the electric-dipole approximation, where the magnetic-field component and the spatial variation of the light electric field over the relevant electronic length scales are both ignored. Non-dipole effects in photoionization were revealed to be tiny from the infrared to the soft X-ray domains, and all non-dipole observations reported so far were limited to single-pulse, single-colour measurements. Here we advance attosecond time-resolved spectroscopy into the non-dipole interaction regime. Using a self-referenced attosecond photoelectron interferometry on helium atoms, we resolve the electron subcycle motion along the light propagation direction in the 15 pm range driven by the magnetic component of a near-infrared laser field. Furthermore, we measure a time delay of 15 ± 10 as between the electric-dipole and electric-quadrupole transitions by resolving the asymmetry of the photoelectron forward–backward yields with attosecond resolution. These fundamental findings are supported by ab initio calculations based on the non-dipole time-dependent Schrödinger equation. Using a self-referenced attosecond photoelectron interferometry on helium atoms, the electron subcycle motion along the light propagation direction is observed in the 15 pm range. A time delay of 15 ± 10 as between the electric-dipole and electric-quadrupole transitions is also revealed. [ABSTRACT FROM AUTHOR]

A poly(toluidine blue) modified glassy carbon electrode (PTB/GCE) was prepared by two-step electropolymerization, and was used for the stripping voltammetric analysis of trace uranium for the first time. The results showed that the PTB modified electrode had higher sensitivity of uranium detection compared with the glassy carbon electrode, and the standard addition method was satisfactory for seawater, river water and tap water. The PTB/GCE can be used as a mercury-free electrode for the electrochemical detection of uranyl ions in the environmental water, which provides a new way for the rapid detection of trace uranium. [ABSTRACT FROM AUTHOR]

New insights are proposed into enhancing detection of uranyl ions (UO22+) by electropolymerization brilliant cresyl blue–modified glassy carbon electrode (PBCB/GCE). The mercury-free PBCB/GCE sensor was applied to determine UO22+ in water samples by differential pulse adsorptive stripping voltammetry (DPAdSV). The unique combination of the PBCB/GCE and DPAdSV significantly improves sensitivity due to the polymer of high electroactive area and fast electron transfer rate. The DPAdSV current using a 3 mm diameter PBCB/GCE was proportional to the UO22+ concentration in the range 2.0–90.0 μg·L−1 (− 0.113 V vs. SCE) with a detection limit of 0.650 μg·L−1, RSD = 3.1% (n = 10), and 4.5% reproducibility. In addition, the sensitivity for UO22+ determination was further improved at using an 1 mm diameter PBCB/GCE, which enhances the efficiency of UO22+ deposition due to its higher current density. The 1 mm diameter PBCB/GCE based on DPAdSV technique could be used to determine uranyl ions in the concentration range 0.20–2.0 μg·L−1 (− 0.113 V vs. SCE) with a detection limit of 0.067 μg·L−1, RSD = 5.7 % (n = 10) and 5.4% reproducibility. Hence, the PBCB/GCE is a suitable candidate to substitute the mercury electrode. [ABSTRACT FROM AUTHOR]

Herein, a novel strategy for sensitive determination of uranium in natural water was proposed using electropolymerization of Nile blue modified glassy carbon electrode (PNB/GCE) and differential pulse adsorptive stripping voltammetry (DPAdSV). The preparation of modified electrodes, electrolyte, reproducibility, and substance interferences was studied. The PNB/GCE were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and DPAdSV. The DPAdSV peak current was proportional to the concentration of uranium in the range of 0.30–100 μg·L−1 with the detection limit of 0.19 μg·L−1 and R2 = 0.997. Finally, the PNB/GCE was successfully applied to determination of uranium in natural water samples. [ABSTRACT FROM AUTHOR]

The Jahn-Teller effect is an essential mechanism of spontaneous symmetry breaking in molecular and solid state systems, and has far-reaching consequences in many fields. Up to now, to directly image the onset of Jahn-Teller symmetry breaking remains unreached. Here we employ ultrafast ion-coincidence Coulomb explosion imaging with sub-10 fs resolution and unambiguously image the ultrafast dynamics of Jahn-Teller deformations of CH 4 + cation in symmetry space. It is unraveled that the Jahn-Teller deformation from C3v to C2v geometries takes a characteristic time of 20 ± 7 fs for this system. Classical and quantum molecular dynamics simulations agree well with the measurement, and reveal dynamics for the build-up of the C2v structure involving complex revival process of multiple vibrational pathways of the CH 4 + cation. The Jahn-Teller effect is the spontaneous symmetry breaking of the molecular structure caused by the coupling of electrons and nuclei. Here the authors use ultrafast Coulomb explosion imaging to map the evolution of the fundamental symmetry lowering process in photoionized methane within around 20fs. [ABSTRACT FROM AUTHOR]

Strong-field tunneling ionization is the first step for a broad class of phenomena in intense laser-atom/molecule interactions. Accurate information about the electron wave packet from strong-field tunneling ionization of atoms and molecules is of essential importance for understanding various tunneling ionization triggered processes. Here, we survey the property of the electron wave packet in tunneling ionization of molecules with a method based on strong-field photoelectron holography. By solving the time-dependent Schrödinger equation, it is shown that the holographic interference in the photoelectron momentum distribution exhibits the asymmetric behavior with respect to the laser polarization direction, when the molecule is aligned with a nonzero angle to the linearly polarized laser field. We demonstrate that this asymmetry is due to the nonzero initial transverse displacement of the electron wave packet at tunneling. By analyzing the holographic interference, this transverse displacement for the launching of electron wave packet tunneling from the molecules is accurately retrieved. This displacement is directly related to the electron density distribution in molecules, and thus our work developed a novel concept for probing electronic structure in molecules. [ABSTRACT FROM AUTHOR]

We use an interferometic scheme to extract the phase distribution of the electron wave packet from above-threshold ionization in elliptically polarized laser fields. In this scheme, an electron wave packet released from a circularly polarized laser pulse acts as a reference wave and interferes with the electron wave packet ionized by a time-delayed counter-rotating elliptically polarized laser field. The generated vortex-shaped interference pattern in the photoelectron momentum distribution enables us to extract the phase distribution of the electron wave packet in the elliptically polarized laser pulse with high precision. By artificially screening the ionic potential at different ranges when solving the time-dependent Schördinger equation, we find that the angle-dependent phase distribution of the electron wave packet in the elliptically polarized laser field shows an obvious angular shift as compared to the strong-field approximation, whose value is the same as the attoclock shift. We also show that the amplitude of the angle-dependent phase distribution is sensitive to the ellipticity of the laser pulse, providing an alternative way to precisely calibrate the laser ellipticity in the attoclock measurement. [ABSTRACT FROM AUTHOR]

Direct and rapid determination of trace amounts of uranium in natural water remains a challenge. Herein, determination of uranium by differential pulse adsorptive stripping voltammetry (DPAdSV) in presence of cupferron and diphenylguanidine on glassy carbon electrode was investigated. Under optimized conditions, the DPAdSV peak current was proportional to the concentration of uranium in the range of 3–80 μg L−1 with the detection limit of 1.0 μg L−1 and a linear correlation coefficient of 0.999. The DPAdSV method based on GCE was successfully applied to direct determination of trace uranium in natural water samples. [ABSTRACT FROM AUTHOR]

By numerically solving the two-dimensional time-dependent Schrödinger equation, we investigate the strong-field photoelectron holography (SFPH) for different atomic and molecular targets. The results show that the photoelectron hologram is capable of providing structural information-the phase of scattering amplitude. In our calculations, the holographic pattern shifts with the target, indicating the phase difference between various targets. However, for the near-forward scattering, the phases of scattering amplitude for different targets are similar and thus no structural information has been retrieved in the previous works on near-forward scattering hologram. We suggest to use the backward scattering photoelectron hologram to extract this type of structural information. This paves a significant step towards time-resolved imaging of molecular structure and dynamics with the concept of SFPH. [ABSTRACT FROM AUTHOR]

With the three-dimensional semiclassical ensemble model, we studied the correlated electron dynamics in strong-field nonsequential double ionization of Xe by mid-infrared laser pulses over a wide range of laser intensities. Numerical results show that the correlated electron momentum distribution exhibits the strong back-to-back pattern at the lower laser intensity. It evolves into the side-by-side behavior as the laser intensity increases and presents the experimentally observed crosslike shape at high laser intensity. Different from the case of near-infrared region where recollision mainly occurs at the first returning, at the mid-infrared region recollision dominantly occurs at the later returnings. The windows of initial transverse velocity for the various multiple-returning recollision trajectories are different and are unambiguously determined by this semiclassical ensemble model. [ABSTRACT FROM AUTHOR]

A modified model is established according to the analysis of energy balance acting on an agglomerate of binary mixed nanoparticles in a vibrated fluidized bed (VFB). The sizes of agglomerates of binary mixed nanoparticles are calculated with this model. The average agglomerate size estimated by the model of energy balance decreases with increasing superficial gas velocity. The vibration frequency had a comparatively significant impact on agglomerate sizes that seemed to change regularly and decreased with higher frequency. Both of the experimental and theoretical results showed that vibration led to a smaller agglomerate size, and the average agglomerate sizes calculated by this model provided the closest fit to those determined experimentally. [ABSTRACT FROM AUTHOR]

Herbicides such as atrazine are widely used in the biosphere. Urine analysis is usually performed to evaluate the toxicological effects associated with atrazine exposure. A simple procedure based on the extractive electrospray ionization mass spectrometry (EESI-MS) method was established to detect atrazine and its metabolites in undiluted raw urine without sample pretreatment. A 4.3 × 10−14 g atrazine in spiked raw urine was detected and identified by EESI/MS/MS/MS. The detection limit was found to be 0.4 fg for atrazine (m/z 174) and 0.2 fg for 2-chloro-4, 6-diamino-S-triazine (DACT) (m/z 129) (S/N = 3) in EESI/MS/MS. A linear dynamic range of 4–5 orders of magnitude (r = 0.996) was determined for both atrazine and DACT. A single sample analysis was completed using tandem EESI-MS/MS within 1 min, providing a practical convenient method for rapid analysis of trace amounts of targeted metabolites present in complex matrices. Thus, tandem EESI-MS is potentially useful for previously discovered biomarker detection in multiple applications such as clinical diagnosis, drug discovery and forensic science. [ABSTRACT FROM AUTHOR]

By numerically solving the time-dependent Schrödinger equation, we theoretically investigate the holographic structure of the multiple-returning rescattering recorded in the photoelectron momentum distribution. In the orthogonally polarized two-color fields, we show that the interference patterns periodically oscillate with the relative phase. Tracing the relative phase where the oscillation minimizes, we find that the dependences of the phase on the parallel momentum for the first-returning and the second-returning rescattering holographic interferences are different. With the quantum-orbit model, we demonstrated that the difference is related to the ionization and rescattering times of the electron. Moreover, we show that the influence of the Coulomb interaction on the oscillation of both the first-returning rescattering and the second-returning rescattering holographic interferences can be ignored. This suggests us that the temporal characteristics of the electron can be resolved by analyzing the relative phase's dependence of the multiple-returning holographic interference. [ABSTRACT FROM AUTHOR]

We calculate the photoelectron momentum distributions (PMDs) from strong-field above-threshold ionization of Ar in the co-linearly polarized two-color laser fields consisting a strong fundamental component and a much weaker second harmonic by solving the time-dependent Schrödinger equation. Utilizing the recently introduced phase-of-the-phase (PP) spectroscopy, we analyze the relative phase dependence of the PMDs of the recollision electrons and the jumps in the PP spectroscopy are observed. With the semi-classical model, we demonstrate that the phase jumps originate from the competition between the orbits where recollision occurs at different returnings. Thus, the relative contribution of the multiple-returning recollision orbits is unambiguously identified with the PP spectroscopy. Additionally, we show that the relative contribution of the multiple-returning recollision orbits depends on the laser wavelength and ellipticity. In elliptically polarized laser field, the yield of the high-energy photoelectrons favors the contribution of the second-returning recollision orbits. In 1600-nm laser field, the PP spectroscopy indicates that the relative contribution of multiple-returning recollision orbits is strongly sensitive to the electron energy. [ABSTRACT FROM AUTHOR]

The partition of the photon energy into the subsystems of molecules determines many photon-induced chemical and physical dynamics in laser-molecule interactions. The electron-nuclear energy sharing from multiphoton ionization of molecules has been used to uncover the correlated dynamics of the electron and fragments. However, most previous studies focus on symmetric molecules. Here we study the electron-nuclear energy sharing in strong-field photoionization of HeH2+ by solving the one-dimensional time-dependent Schrödinger equation (TDSE). Compared with symmetric molecules, the joint electron-nuclear energy spectrum (JES) of HeH2+ reveals an anomalous energy shift at certain nuclear energies, while it disappears at higher and lower nuclear energies. Through tracing the time evolution of the wavepacket of bound states, we identify that this energy shift originates from the joint effect of the Stark shift, associated with the permanent dipole, and the Autler-Townes effect due to the coupling of the 2pσ and 2sσ states in strong fields. The energy shift in the JES appears at certain nuclear distances only when both Stark effect and Autler-Townes effect play important roles. We further demonstrate that the electron-nuclei energy sharing can be controlled by varying laser intensity for asymmetric molecules, providing alternative approaches to manipulate photochemical reactions for more complex molecules. [ABSTRACT FROM AUTHOR]