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Angular interferences of sequentially ionized double-continuum wave packets
摘要： Following the recent report of energy and angle interferences in below-threshold photoexcitation Auger processes due to postcollision interactions [Wang and Robicheaux, Phys. Rev. A 98, 013421 (2018)], similar interferences are also found in double-continuum wave packets from a two-step time-delayed photoionization of a two-electron atom. Properties of the interferences are studied in detail with respect to laser pulse time widths, laser frequency chirping, and ionization time delay. The effects of these physical quantities on the resulting interferences are discussed.
关键词： angular interferences,photoionization,frequency chirping,laser pulse,double-continuum wave packets,ionization time delay
更新于2025-09-11 14:15:04
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Partial Photoionization Cross Section of Collinear eZe Helium: Numerical Confirmation of Semiclassical Predictions
摘要： Based on the semiclassical theory of chaotic scattering, Tanner et al. [J. Phys. B 40, F157 (2007)] proposed the fluctuation in the partial photoionization cross section of helium below the double-ionization threshold would show the same characteristics as in the total cross section, predicting that the Fourier spectrum of the fluctuation reveals peaks at the classical actions of closed triple collision orbits and the amplitude of the fluctuation decreases algebraically as the energy approaches the double-ionization threshold. In that paper, however, the predictions were not clearly confirmed due to the lack of experimental data with sufficient accuracy. So instead, we calculate the partial photoionization cross sections of collinear eZe helium for the energy range from the single-ionization threshold I20 to I32 in order to numerically confirm the predictions. Analysis of the fluctuation in the partial cross section shows that the predictions are indeed valid. Our findings mean that the fluctuation in the partial photoionization cross section can be described by classical triple collision orbits in the semiclassical limit. Thus it explains in a natural way the mirroring and mimicking structures observed in cross section signals for different ionization channels.
关键词： Partial photoionization cross section,Collinear eZe helium,CTCO,Scaling law
更新于2025-09-10 09:29:36
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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Photoionization
摘要： The ionization of analyte molecules is of vital importance to mass spectrometric analysis because mass spectrometry takes only ions as the object for analysis. The most commonly used ionization source in mass spectrometry is electron-impact (EI) ionization source with electrons impacting to analyte with an energy of 70 eV. The kinetic energy of 70 eV is much higher than the ionization energy of organic molecules, and the ionization process approaches the maximal ionization efficiency. Thus, a large number of fragment peaks are usually observed in an EI mass spectrum. These fragments act as fingerprints of molecules, which can be used for identification of unknown molecules by searching EI-MS library, for example NIST Mass Spectral Library. This statistically based identification is particularly convenient and effective when analyzing a single component, for example a preseparated analyte by GC. However, there are many cases that analytes cannot be preseparated, for example very active components in a reaction, or fast on-line observation of evolving analytes. Consequently, the extensive fragmentation by EI-MS turns to a severe disadvantage: if each compound of a mixture produces a certain amount of fragment peaks, serious interference can be made, which will bring muscular obstacles to peak assignment. The best strategy is to use a “soft” ionization source with high selectivity. Here, “soft” means fragment-free or fragment-controllable.
关键词： SPI,Photoionization,APPI,REMPI,VUV Lamps,Synchrotron Radiation,Lasers,Mass Spectrometry
更新于2025-09-10 09:29:36
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Vibronic structure and photoelectron angular distribution in the photoelectron spectrum of ICN
摘要： The valence shell photoelectron spectrum of ICN has been simulated using the equation-of-motion coupled-cluster method to calculate the ionization energies and the norms of the Dyson orbitals to describe the intensity of the photoelectron bands. The simulated spectrum not only reproduces the position and intensity of the four main bands observed in the experimental photoelectron spectrum, but the vibronic structure present in the individual photoelectron bands is also reproduced to a reasonable extent. The agreement between the experimental and simulated vibronic structures at higher energies corresponding to the ?A and ?B states is particularly noteworthy. Additionally, the photoionization cross section and asymmetry parameter have been calculated for the ionization of four outermost valence molecular orbitals in the photon energy range of 0–50 eV. The computed asymmetry parameters are found to provide a qualitative description of the corresponding experimental measurements. The shape-resonance seen in the experimental asymmetry parameters and the trends seen in the calculated cross section for the four ionization channels have been explained by the partial wave analysis of the contribution of the individual angular momentum channels to the photoelectron.
关键词： ICN,photoelectron spectrum,vibronic structure,equation-of-motion coupled-cluster method,Dyson orbitals,asymmetry parameter,photoionization cross section
更新于2025-09-10 09:29:36
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Dissociation dynamics of the water dication following one-photon double ionization. I. Theory
摘要： The measurement of the triple differential cross section in the body frame for double photoionization of a molecule can be made in principle by detecting the ionic fragments and the two photoelectrons in coincidence—but only if the dynamics and geometry of dissociation of the doubly charged molecular ion are known. A classical trajectory study of the nine lowest states of the water dication is presented using high quality ab initio potential-energy surfaces. Sampling from a semiclassical initial distribution of positions and momenta is used to approximate ionization from the Frank-Condon region of the ground vibrational state of neutral H2O. Excellent agreement in comparison with preliminary experimental momentum imaging measurements of double photoionization of water show that eight dication states can be unambiguously identified in the experiment with the aid of theory. The theoretical trajectory results allow body frame measurements of double photoionization to yield all eight states even though the usual assumption of direct dissociation, the “axial recoil” approximation, breaks down for three of the dication electronic states seen in the experiment.
关键词： potential-energy surfaces,double photoionization,dissociation dynamics,classical trajectory study,water dication
更新于2025-09-09 09:28:46
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Quantum interference in the femtosecond photoionization spectra of NaI molecules
摘要： This study investigates femtosecond pump–probe photoionization of NaI molecules by solving the time-dependent Schr?dinger equation?through the wave packet approach. The photoelectron spectra are presented to analyze the dynamic information of the internal wave packet. Quantum interference is observed in the photoelectron kinetic energy spectrum at a certain time delay of the probe field. The interference signals are weak but cover a wide range of energy. This finding is consistent with the interfering process of forward and returned wave packets at short internuclear distances of the repulsive potential.
关键词： photoionization,quantum interference,Wave packet dynamics,photoelectron spectrum
更新于2025-09-09 09:28:46
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Low-Energy Photoelectron Spectrum and Dissociative Photoionization of the Smallest Amides: Formamide and Acetamide
摘要： The threshold photoelectron spectrum and low-energy dissociative photoionization processes of formamide and acetamide were studied using photoelectron photoion coincidence spectroscopy and vacuum ultraviolet synchrotron radiation. Ab initio calculations and Franck–Condon simulations helped us assign the main vibrational progressions in the spectra and enabled the first conclusive assignment of the first electronically excited states. The adiabatic ionization energies to the ???+ and ???+ states of formamide (10.236 ± 0.004 eV and 10.643 ± 0.015 eV) and acetamide (9.734 ± 0.008 and 10.282 ± 0.020 eV) have been re-evaluated and spectroscopic transitions were assigned using a Franck–Condon approach. The cationic potential energy surface was explored to rationalize the observed fragmentation patterns and to construct a statistical model, which was fitted to the experimental breakdown diagram. Thermochemical thresholds were measured and calculated for H, CO, and NH2 loss from HCONH2+ as well as for CH3, NH2, CO, HCCO, and NH3 loss from CH3CONH2+. We present the first comprehensive, experimental and theoretical treatise of these fragmentation processes. The statistical model confirms fast internal conversion between the ???+ and ???+ states in formamide, as H-transfer in CO loss is shown to take place on the excited state surface. It also explains the five almost simultaneously opening dissociation channels in the acetamide cation quantitatively. The derived 0 K appearance energies have been confirmed by ab initio calculations and by comparison with state-of-the-art thermochemical data, and revise some of the previous results by more than ten times their stated uncertainty.
关键词： Dissociative Photoionization,Photoelectron Spectrum,Acetamide,Formamide,Quantum Chemistry,Spectroscopy,Molecular Structure
更新于2025-09-09 09:28:46
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Circular dichroism in photoionization of degenerate orbitals: Spin-polarized photoelectrons and spontaneous separation of oriented photoions
摘要： This work investigated the circular dichroic effect on the photoionization integral cross section of molecules in conjunction with irreducible tensor theory and effective operator formalism. The results show that the dichroic effect can be non-zero for complex orbitals, but becomes zero for all real orbitals due to time-reversal symmetry, within the electric dipole and Born-Oppenheimer approximations. Calculations were performed for carbon monoxide, boric acid, and fullerene, and implications of the first-order coefficient for the spin polarization of photoelectrons and the molecular axis orientation of photoions are discussed herein. The results of this work demonstrate that the photoionization of complex orbitals can cause photoions to become oriented such that photoions originating from complex conjugate orbitals are oriented opposite to one another. Due to electron-ion recoil, the spontaneous separation of these two kinds of photoions is expected for the point groups Cn, Cnv, C∞v, Cnh, and Sn with n ≥ 3.
关键词： degenerate orbitals,photoionization,oriented photoions,spin-polarized photoelectrons,circular dichroism
更新于2025-09-09 09:28:46
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Spectroscopic diagnostics of low-ionized iron-peak elements. Electron-impact excitation of Ni3 + and photoionization of Ni2 +.
摘要： The spectra from Fe-peak elements may be used to determine the temperature and density of various astrophysical objects. Determination of these quantities is underpinned by the accuracy and the comprehensiveness of the underlying atomic structure and collisional calculations. In the following paper, we shall focus specifically on Ni iv lines associated with transitions amongst several low-lying levels. We shall employ modified versions of the parallel Dirac R-matrix codes, considering both electron-impact excitation of Ni3+ and the photoionisation of both the ground and excited states of Ni2+. We produce high-quality data sets for both processes, and using these data, we calculate line ratios relevant for plasma diagnostics of temperature and density.
关键词： opacity,Atomic data,electron-impact excitation,photoionization
更新于2025-09-04 15:30:14
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A vacuum ultraviolet photoionization time-of-flight mass spectrometer with high sensitivity for study of gas-phase radical reaction in a flow tube
摘要： Photoionization mass spectrometry as a powerful analytical method has been widely utilized and provided valuable insight in the field of gas-phase reactions. Here, a highly sensitive vacuum ultraviolet (VUV) photoionization time-of-flight mass spectrometer combined with a microwave discharge generator and a fast flow tube reactor has been developed to study radical reactions of atmospheric and combustion interests. Two kinds of continuous light sources, the tunable VUV synchrotron radiation at Hefei, China for isomer-specific product detection and a commercial krypton discharge lamp for time-consuming kinetic measurements, are employed as photoionization sources in the apparatus. A multiplexed detection with high sensitivity (the limit of detection ～0.8 ppb) and high mass resolution (M/ΔM ～ 2100) has been approached. As representative examples, the self-reaction of the methyl radical, CH3, and the reaction of the methyl radical with molecular oxygen are studied and multiple species including reactive radicals and isomeric/isobaric products are detected and identified. In addition, some preliminary results related to the reaction kinetics are also presented.
关键词： methyl peroxy radical,kinetics,flow tube,Photoionization mass spectrometer,methyl radical,radical reaction
更新于2025-09-04 15:30:14