Electron-impact excitation of the 3s'3P° and 2s2p53P° autoionizing states of atomic oxygen

The excitation of the 3s''³P° and 2s2p⁵³P° autoionizing states of OI by electron impact on atomic oxygen has been studied. Absolute cross section values from threshold to 300 eV have been obtained for the 3s''³P° state. Limited emission cross section data for the 2s2p⁵³P° and other partially radiating autoionizing states were also obtained at an impact energy of 100 eV. These results suggest that the excitation of the OI autoionizing states account for ≈33% of the total O⁺ total ionization cross section at 40 eV under optically thin conditions and that the cross section ratio, σ(⁴S)/σ(²D + ²P), has been underestimated substantially in earlier theoretical work. Electron-impact excitation of the 3s''³P° and 2s2p⁵³P° states in an optically thick medium enhances the effective total ionization cross section for atomic oxygen by ≈15% and increases the specific O⁺(⁴S) production rate by ≈25% with important implications for O⁺ ion chemistry in gaseous discharges and planetary ionospheres.     

Investigation of autoionizing CuI-states in the region of the second ionization limit CuII 3d 94s

The combination of collisional and laser excitation was used for the investigation of autoionizing CuI states in the region of the second ionization limit CuII 3d ⁹ 4s at 85000–95000 cm^?1. The analysis of the complicated signal structure was concentrated on the first measurement of CuI 3d ⁹ 4p ² levels. The experimental results are compared with Hartree-Fock calculations of the energy values and level widths of the autoionization resonances.     

Low-energy electron impact excitation of the lowest-lying autoionizing level in Li

We have calculated the electron impact total cross sections for the excitation of the lowest-lying autoionizing level generated due to the core- excitation 1s²2s²S^e å 1s2s²²Se transition in the lithium atomic system using Hartree—Fock wave-functions for both initial and final states within the R-matrix method in the low bombarding energy region. Our results show that the energy dependence of cross sections is significantly different in nature from all earlier theoretical predictions.     

Two-photon ionization of an inner shell electron of the Cl atom

We have calculated, using second order perturbation theory, the two photon ionization cross section of a K-shell electron of chlorine forE=1.6 keV incident photons. Two classes of intermediate states must be considered, those in which a 1s electron moves to an emptyp-orbital, and those in which an electron from an occupiedp-orbital moves into the continuum. The first class of intermediate states is followed by the ejection of ap-electron into the continuum. The second class of intermediate states is followed by the transfer of a 1s electron into an emptyp-state. The largest contribution comes from 3p →d-continuum followed by 1s → 3p transition. Our result is σ⁽²⁾/I=2.06×10⁴¹ cm⁴/W where σ⁽²⁾ is the two photon ionization cross-section andI is the light intensity.     

Investigation of laser induced structures in multiphoton ionization of magnesium

We examine the effect of the excitation of an autoionizing state on electron spectra resulting from multiphoton-ionization. We study the case of above threshold three-photon ionization of magnesium in the region of the 3p3d ¹ P ⁰ resonance, with conditions similar to a two-colour experiment recently performed. The electron spectrum is compared to the partial spectrum corresponding to the region located just above the threshold (which is populated through two-photon absorption from a probing laser). The calculations confirm the experimental observations, a laser induced continuum structure (LICS) is observed in this partial spectrum. The interference process in examined in detail and a Fano-like parametrization of the two-photon ionization electron profile is proposed.     

Theoretical study of LiK and LiK+ in adiabatic representation

The potential energy curves have been calculated for the electronic states of the molecule LiK within the range 3 to 300 a.u., of the internuclear distance R. Using an ab initio method, through a semiempirical spin-orbit pseudo-potential for the Li (1s ²) and K (1s ²2s ²2p ⁶3s ²3p ⁶) cores and core valence correlation correction added to the electrostatic Hamiltonian with Gaussian basis sets for both atoms. The core valence effects including core-polarization and core-valence correlation are taken into account by using an l-dependent core-polarization potential. The molecular orbitals have been derived from self-consistent field (SCF) calculation. The spectroscopic constants, dipole moments and vibrational levels of the lowest electronic states of the LiK molecule dissociating into K (4s, 4p, 5s, 3d, and 5p) + Li (2s, 2p, 3s, and 3p) in ^{1, 3}Σ, ^{1, 3}Π, and ^{1, 3}Δ symmetries. Adiabatic results are also reported for ²Σ, ²Π, and ²Δ electronic states of the molecular ion LiK⁺ dissociating into Li (2s, 2p, 3s, and 3p) + K⁺ and Li⁺ + K (4s, 4p, 5s, 3d, and 5p). The comparison of the present results with those available in the literature shows a very good agreement in spectroscopic constants of some lowest states of the LiK and LiK⁺ molecules, especially with the available theoretical works. The existence of numerous avoided crossing between electronic states of ²Σ and ²Π symmetries is related to the charge transfer process between the two ionic systems Li⁺K and LiK⁺.     

Lifetime measurements and stark mixing of autoionizing Cu I-states

Using a combination of collisional and laser excitation the lifetimes of 17 autoionizing Cu I states in the configurations 3d ⁹ 4s 6s and 3d ⁹ 4s4d were measured. The lifetimes are in the range of 1–50 ps and depend strongly on the coupling properties, the mixing with different configurations, and the radial integrals of the discrete with the continuum states. For the level 3d ⁹ 4s 4d ⁴ S _3/2 the influence of an electric field via Stark mixing of 3d ⁹ 4s 5p ⁴ P _1/2 on the autoionizing rate was investigated. The experimental values are compared with theoretical results which follow from ab initio calculations for the transition probabilities and least square fit values deduced from the experimental positions. Good agreement is found only for theJ=3/2 levels of both configurations 3d ⁹ 4s 4d and 3d ⁹ 4s 6s.     

Alignment of atomic autoionizing states created by slow Na++He collisions

Ejected-electron spectra have been measured for collisions of He-atoms with Na⁺-ions, whose impact energy ranged from 1.7 to 7.0 keV. The ion impact-energy dependence of the angular-differential cross-section of the ejected electrons has been investigated for an aligned autoionizing state Na**(2p ⁵ 3s ^{2 2} P), which has been created by charge transfer from the He-atoms. The alignment of the autoionizing state Na**(2p ⁵ 3s ^{2 2} P) is discussed in relation to the scattering angles of the Na⁺-ions. A complete longitudinal alignment has been observed with respect to the quasimolecular axis.     

Detection of the even parity,J=0–3, autoionizing 4dnl Rydberg states of strontium by two-step laser optogalvanic spectroscopy

We have measured the energies of a few hundreds of even parity,J=0–3 autoionizing 4dnl Ry states of strontium using an optogalvanic spectroscopy technique. These states are reached by a two-step pulsed dye laser excitation from the 4d 5s metastables through the 4d 5p ³P_0,1,2 intermediate states. Electronic collisions populate the 4d 5s states in a d.c. glow discharge through a Sr plus He vapour in a heated quartz cell. The electronic configuration for the majority of the observed Sr states is deduced from their quantum defect values and other characteristics of the corresponding transitions.     

Resonance-enhanced photon excitation spectroscopy of the even-parity autoionizing Rydberg states of Kr

Kr atoms were produced in their metastable states 4p⁵5s [3/2]₂ and 4p⁵5s’ [1/2]₀ in a pulsed DC discharge in a beam, and subsequently excited to the even-parity autoionizing Rydberg states 4p⁵ np′ [3/2]_1,2, [1/2]₁ and 4p⁵ nf′ [5/2]₃ using single photon excitation. The excitation spectra of the even-parity autoionizing resonance series from the metastable Kr were obtained by recording the autoionized Kr⁺ ions with time-of-flight ion detection in the photon energy range of 29000–40000 cm⁻¹. A wealth of autoionizing resonances were newly observed, from which more precise and more systematic spectroscopic data of the level energy and quantum defects were derived. Supported by the National Natural Science Foundation of China (Grant No. 20673107), the National Key Basic Research Special Foundation of China (Grant No. 2007CB815203), and Chinese Academy of Sciences (Grant No. KJCX2-SW-H08)     

Line-profile analysis of excitation spectroscopy in the even 4p5(2P1/2)nl′ [K′]J（l′=1,3） autoionizing resonances of Kr

The even-parity autoionizing resonance series 4p5np′[3/2]1,2,[1/2]1,and 4p5nf′[5/2]3of krytpon have been investigated by laser excitation from the two metastable states 4p55s[3/2]2and 4p55s′[1/2]0in the photon energy region of 29000–40000 cm 1at experimental bandwidth of~0.1 cm 1.The excitation spectra of the even-parity autoionizing resonance series,most of which are experimentally studied for the first time in this work,show typical asymmetric line shapes.Complementary information on level energies,quantum defects,line profile indices and resonance widths,resonance lifetimes and reduced widths of the autoionizing resonances are derived by Fano-type line-shape analyses of the experimental results.Results from this work indicate that the line profile index(q)and the resonance width()are approximately proportional to the effective principal quantum number(n*);the line separation of the 4p5np′autoionizing resonances is also in good agreement with theoretical model.     

Two-step laser optogalvanic spectroscopy of highJ momentum 4dnd and 4dng autoionizing states of strontium

We have measured the energies of about two hundred even parityJ=3–5 autoionizing 4dnd and 4dng Rydberg states of strontium (Sr) using an optogalvanic method. These states are reached by a two-step dye laser excitation from the 4d5s metastables through the 4d5p ³ P ₂,¹ F ₃,³ F ₄ intermediates. The 4d5s are populated in a d.c. glow discharge through a Sr heated cell. The electronic configuration of the observedJ=3, 4 states is deduced from the Lu-Fano plots of their quantum defect values and the spectral characteristics of the corresponding transitions.     

Experimental and Theoretical Investigation of the 3sp(d) Rydberg States of Fenchone by Polarized Laser Resonance-Enhanced-Multiphoton-Ionization and Fourier Transform VUV Absorption Spectroscopy

The VUV absorption spectrum of fenchone is re-examined using synchrotron radiation Fourier transform spectrometry, revealing new vibrational structure. Picosecond laser (2+1) resonance enhanced multiphoton ionization (REMPI) spectroscopy complements this, providing an alternative view of the 3spd Rydberg excitation region. These spectra display broadly similar appearance, with minor differences that are largely explained by referring to calculated one- and two-photon electronic excitation cross-sections. Both show good agreement with Franck-Condon simulations of the relevant vibrational structures. Parent ion REMPI ionization yields with both femtosecond and picosecond excitation laser pulses are studied as a function of laser polarization and intensity, the latter providing insight into the relative two-photon excitation and one-photon ionization rates. The experimental circular-linear dichroism observed in the parent ion yields varies strongly between the 3s and 3p Rydberg states, in good overall agreement with the calculated two-photon excitation circular-linear dichroism, while corroborating other evidence that the 3p_z sub-state plays no more than a very minor role in the (2+1) REMPI spectrum. Vibrationally resolved photoelectron spectra are recorded with picosecond pulse duration (2+1) REMPI at selected intermediate vibrational excitations. The 3s intermediate state displays a very strong Δv=0 propensity on ionization, but the 3p intermediate evidences more complex vibronic dynamics, and we infer some 3p→3s internal conversion prior to ionization.     

Coupling between autoionizing states in atomic strontium

I present a theory and calculations of transitions between autoionizing states in Sr. Such transitions are found to become significant at photon fluxes above 10²⁹ photons/cm² s and tend to leave the ion in excited states. Examples of transitions to the excited ionic states 4d and 5p are presented. Their dependence on laser intensity is found to be quite intricate.     

Photoionization of the 2s, 2p and 3s subshells of Mg+

We present calculations of total and partial photoionisation cross sections for the 2s, 2p and 3s subshells of Mg⁺ from their ionisation thresholds up to a photon energy of 220 eV. Photoelectron angular distribution parameters are also calculated for the 2p subshell. Oscillator strengths are given for discrete structure, and calculated energy levels compared with experimental values. The significance of electron correlations and two electron excitation for this atomic ion is discussed.     

Quantum chemical ab initio calculations for excited states of F IV

Quantum chemical ab initio calculations have been performed for the ground state and for several excited states of the F³⁺ ion (F IV). Three levels of accuracy have been used: Frozen-core SCF calculations (FRC-SCF) to determine orbital energies ε _nl and quantum defects δ _l for excited Rydberg orbitalsnl; frozen-core SCF followed by CI calculations (FRC-CI) which account for multiplet splittings and configuration mixings, and multi-configuration coupled-electron-pair approximation (MC-CEPA) calculations which include dynamic correlation effects. The accuracy of the calculated excitation energies is in the order of 5000 cm^?1 at the FRC-CI level and in the order of 500 cm^?1 at the MC-CEPA level. This latter error amounts to about 0.1% for excitation energies in the range of 400000 to 600000 cm^?1. The MC-CEPA calculations have been performed for 17 experimentally known states and for 14 experimentally unknown states, in particular for the configurations 2s2p ² (² D)3s, 2s 2p ²(² S)3s, 2s ² 2p 4p, and 2s ² 2p 5p.     

Theory of single and double ionization of helium through two-photon excitation of the1 S 0 e (1) doubly excited resonance

We present a theory and calculations of two-photon-resonant three-photon ionization of He via the lowest even parity doubly excited state¹ S ₀ ^e (1). We assess the importance of double ionization relative to single ionization into excited ionic states. Although double ionization is found to be quite small in the present context, our calculations reveal the importance of autoionizing doubly excited states as virtual intermediate states and suggest contexts in which double ionization may be relatively more efficient.     

Alignment of atomic autoionizing states created by slow Li++Ne collisions

Ejected-electron spectra have been measured in collisions of Ne-atoms with Li⁺-ions, whose impact energy has been ranged from 0.4 to 7.0 keV. The ion impact-energy dependence has been investigated on the angular-differential cross-section of the ejected electrons from the aligned autoionizing state Ne** 2p ⁴3s ^{2 1} D. In the highest energies studied, cross section maxima have been found at both forward and backward angles with respect to the Li⁺-ion beam direction, whereas the cross sections are maximized at around right angles below intermediate energies. The data were analyzed semi-quantitatively, and the alignment of the autoionizing state was recognized to be characterized by a representative scattering angle of the Li⁺-ions.     

CO inner-shell excitation studied by electron impact spectroscopy

The inner-shell excitation and decay of the CO molecule have been studied in electron impact experiments. The dipole-forbidden transition (1sσ_c)⁻¹(2pπ) ³Π has been characterized by angular resolved electron energy loss spectroscopy and its decay via the measurement of resonant Auger spectra. The contribution of the (1sσ_c)⁻¹(2pπ) ³Π state to the CO resonant Auger spectrum in the region of the “spectator transitions” has been isolated and the population of CO⁺ quartet final states has been observed.     

3dnl J=3e autoionizing levels of calcium: observation by laser optogalvanic spectroscopy and theoretical analysis

The even parityJ=3 autoionizing spectra of calcium were investigated below the 3d threshold by a two-step laser excitation from the 3d4s metastables through the 3d4p ³ P ₂,¹ F ₃ intermediate states. The 3d4s were populated by electronic collisions in a d.c. glow dis-charge through a Ca heat-pipe. More than a hundred resonance transitions have been measured with an accuracy of ～0.2 cm^?1 for the narrow ones using standard laser calibration techniques. Their upper levels are assigned to all expected nine autoionizing 3dns, 3dnd and 3dng Rydberg series and the 4p 5p ³ D ₃ perturber. The theoretical interpretation is achieved by a combination of the eigenchannelR-matrix and mulitchannel quantum defect (MQDT) methods. Ten closed and two openJ=3 interacting channesl are used. Theoretical energy level positions and excitation profiles are compared with the experimental data confirming the identification of the observed structures. Strong mixing between the 3d _3/2 nd _5/2 and 3d _5/2 nd _3/2 series is found, while the 3d _3/2 nd _3/2 and 3d _5/2 nd _5/2 series are almost purejj-coupled. The calculations were particularly successful in reproducing the spectrum in the region of the 4p 5p ³ D ₃ perturber, where strong chancel mixing appears leading to interference effects in the excitation cross sections.