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Pathways to excitation of atoms with bicircular laser pulses
摘要： We study the excitation of the hydrogen atom by bichromatic circularly polarized laser pulses using numerical solutions of the time-dependent Schr?dinger equation. The results are in agreement with the selection rules for multiphoton processes in such fields, namely, excited states are populated in which orbital angular momentum and magnetic quantum numbers are either both odd or both even, independent of the relative helicity, peak intensity, and pulse duration of the pulses. For co-rotating pulses the results show that excitation predominantly proceeds to states with magnetic quantum number of the same helicity as the laser pulses. Besides pathways via direct photon absorption from the ground state our results indicate that a transfer of population among the Rydberg states occurs via (cid:2)-type transitions. In the case of counter-rotating pulses the largest excitation probability is found for Rydberg states that differ in magnetic quantum number by (cid:3)m = ±3. This pattern allows us to estimate how many photons from each of the two bichromatic fields have been absorbed. Finally, we confirm that a population in Rydberg states beyond a maximum orbital angular quantum number is unlikely.
关键词： Rydberg states,hydrogen atom,bichromatic circularly polarized laser pulses,time-dependent Schr?dinger equation,multiphoton processes
更新于2025-09-23 15:21:01
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Formation of Quantum Vortices at the Ionization of an Atom by an Ultrashort Laser Pulse: Two- and Three-Dimensional Cases
摘要： Quantum vortices formed at the barrier-suppression ionization of an atom by an ultrashort laser pulse have been studied theoretically and numerically. The ionization of a hydrogen atom is considered in the two-dimensional space and the ionization of an atom in the zero-range potential approximation is considered in the three-dimensional space. The resulting analytical expressions imply that the localization of quantum vortices in the three-dimensional space can be predicted by analyzing the two-dimensional model.
关键词： hydrogen atom,zero-range potential approximation,ultrashort laser pulse,Quantum vortices,barrier-suppression ionization
更新于2025-09-23 15:19:57
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Absolute density measurement of hydrogen atom in inductively coupled Ar/H2 plasmas using vacuum ultraviolet absorption spectroscopy
摘要： The absolute density measurement of atomic species such as hydrogen is crucial for plasma processing because of their strong chemical reactivity. In this work, to measure the hydrogen atom density in Ar/H2 inductively coupled plasmas (ICP), the self-absorption-applied vacuum ultraviolet absorption spectroscopy (VUVAS) is studied with a micro-hollow cathode H2/He discharge lamp (MHCL) emitting VUV light (Lyman alpha line; Lα 121.56 nm). The absolute density of hydrogen atoms in the ICP is investigated for various powers (50 W–850 W) in the low pressure region (30 mTorr–50 mTorr). The hydrogen density in remote plasma region is shown to vary from 2.1 × 1011 cm?3 to 1.25 × 1012 cm?3 with respect to plasma power.
关键词： VUV absorption spectroscopy,Low-pressure,Self-absorption,Hydrogen atom density,inductively coupled plasma
更新于2025-09-23 15:19:57
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Attosecond Dynamics of Photoexcitation of the Hydrogen Atom by Ultrashort Laser Pulses
摘要： The dynamics of photoexcitation of the hydrogen atom in the discrete and continuous spectra under the action of laser pulses in the attosecond range of time and pulse durations has been analyzed using perturbation theory. It is shown that over time interval shorter than or on the order of pulse duration, the time dependence of the photoexcitation probability is generally oscillating by nature. It has been established that for certain values of parameters, the envelope of this dependence has a peak, the position of which is determined by the pulse duration and carrier frequency.
关键词： Perturbation theory,Photoexcitation,Hydrogen atom,Attosecond dynamics,Ultrashort laser pulses
更新于2025-09-23 15:19:57
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Photoredox catalyzed generation of acetonyl radical in flow: theoretical investigation and synthetic applications
摘要： A Hydrogen Atom Transfer (HAT) step from acetone allowed the smooth generation of acetonyl radical, that was then exploited as synthon in the mild formation of C–C bonds under flow conditions. The process was promoted by aryl radicals photocatalytically generated via Single Electron Transfer (SET) reduction of arenediazonium salts. The mechanism has been investigated by a combined experimental and computational approach and further supported by deuterium labelling experiments.
关键词： Arenediazonium salts,Hydrogen Atom Transfer (HAT),Acetonyl radical,Photocatalysis,Aryl radicals
更新于2025-09-19 17:15:36
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Evidence of ac-Stark-shifted resonances in intense two-color circularly polarized laser fields
摘要： We report on the appearance of a structure at low energies in the photoelectron momentum distribution of the hydrogen atom exposed to two-color counterrotating bicircular laser fields. These structures, which arise due to ac-Stark-shifted resonances, break the threefold symmetry, typical for the ω ? 2ω bicircular fields. We discuss the physical origin of this structure in terms of partial-wave interference between direct ionization channels and a resonant pathway, which passes through the ac-Stark-shifted state, and show how the underlying Rydberg state population depend on the field strength and pulse duration.
关键词： bicircular laser fields,Rydberg state population,ac-Stark-shifted resonances,photoelectron momentum distribution,hydrogen atom
更新于2025-09-19 17:13:59
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Photoinduced reversible isomerization of 9H-fluorene into 1H-fluorene by means of hydrogen-atom migration and the lowest electronically excited triplet state studied by matrix-isolation FTIR spectroscopy
摘要： Photoinduced reversible intramolecular hydrogen-atom migration between 9H-?uorene and 1H-?uorene isolated in an Ar matrix is found by FTIR spectroscopy with an aid of DFT calculation. The forward isomerization from 9H-?uorene to 1H-?uorene occurs upon UV irradiation (λ ≥ 295 nm), while the backward isomerization occurs upon λ ≥ 320 nm light irradiation. The less stable isomer, 1H-?uorene, is identi?ed by comparison of the measured IR spectrum with the corresponding simulated spectral pattern obtained at the B3LYP/6-31++G(d,p) level. In addition, an IR spectrum of 9H-?uorene in the T1 state is measured during UV irradiation (λ ≥ 275 nm).
关键词： Electronically excited T1 state,Fluorene,Matrix-isolation infrared spectrum,Photoinduced hydrogen-atom migration
更新于2025-09-11 14:15:04
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Photosensitization and Photocatalysis - Perspectives in Organic Synthesis
摘要： Photochemical sensitization and photocatalysis have very similar definitions and are closely related. Each of the two terms are preferentially used in different scientific communities. Three types of processes are discussed: (1) sensitization involving energy transfer, (2) photocatalysis in which hydrogen abstraction plays a key role and (3) photoredox catalysis in which electron transfer is involved. The processes are discussed in connection with [2+2] photocycloadditions and C-H activation, which are of particular interest for organic synthesis.
关键词： [2+2] Photocycloaddition,Photosensitization,Energy transfer,Hydrogen atom transfer,Electron transfer,C-H activation,Photocatalysis
更新于2025-09-09 09:28:46