3PJ States Research Articles

Electronic Rearrangements and Angular Momentum Couplings in Quantum State-to-State Channels of Prototype Oxidation Processes.

An innovative theoretical method to describe the microscopic dynamics of chemi-ionization reactions as prototype oxidation processes driven by selective electronic rearrangements has been recently published. It was developed and applied to reactions of Ne* atoms excited in their metastable 3PJ state, and here, its physical background is extensively described in order to provide a clear description of the microscopic phenomenon underlying the chemical reactivity of the oxidative processes under study. It overcomes theoretical models previously proposed and reproduces experimental results obtained in different laboratories. Two basic reaction mechanisms have been identified: (i) at low collision energies, a weakly bounded transition state is formed which spontaneously ionizes through a radiative physical mechanism (photoionization); (ii) in the hyperthermal regime, an elementary oxidation process occurs. In this paper, the selectivity of the electronic rearrangements triggering the two mechanisms has been related to the angular momentum couplings by Hund’s cases, casting further light on fundamental aspects of the reaction stereodynamics of general interest. The obtained results allow peculiar characteristics and differences of the terrestrial oxidizing chemistry compared to that of astrochemical environments to be highlighted.

Overall and state-specific electronic quenching of atomic sulfur S(3p34p 3PJ) by collisions with He

Atomic sulfur in the electronic ground state 3p43P2 was excited to the 3p34p 3P2 state by two-photon excitation at 308 nm and the vacuum ultraviolet (VUV) fluorescence via the 3p34s 3S → 3p43PJ transition at 180 nm was observed. The time-resolved VUV fluorescence was recorded at varying pressures of He. A kinetic analysis by the integrated profiles method gave the rate coefficient for overall quenching of the 3p34p 3PJ state by collisions with He. The He pressure dependence of the VUV fluorescence intensity averaged in time has derived the branching ratio of the state-specific quenching from the 3p34p 3PJ state to the 3p34s 3S state.

Fock-space multireference coupled cluster calculations of Auger energies of noble gas elements using relativistic spinors.

We report the Auger and Coster-Kronig transition energies (related to double ionization potentials) of noble gas elements obtained using the Fock-space multireference coupled cluster (FSMRCC) method with relativistic spinors. The resulting Auger and Coster-Kronig lines are found to be in agreement with the experimental data and with other reference theoretical estimates. To the best of our knowledge, no prior report of relativistic calculations is available for Auger transition energies at the FSMRCC level of theory. The ionization potentials resulted from this method with no extra cost are also found to be in agreement with experiment, particularly the outer-valence ones. Interestingly, the FSMRCC and the multiconfiguration Dirac-Fock calculations exhibit an inversion in the 3P energy levels of the xenon atom for N4,5-O23O23 Auger transitions, where the 3Pj state energies appear in the order J = 1, 0, 2, a feature which can be verified experimentally.

Saturated fluorescence spectroscopy measurement apparatus based on metastable Li+ beam with low energy.

The apparatus for fluorescence spectroscopy measurement is developed to determine the fine structure (FS)/hyperfine structure (HFS) splittings of 1s2p 3PJ(J=0,1,2) states of Li+. The instrument is composed of a low energy Li+ ion source and a saturated fluorescence spectroscopic probing system. A low energy Li+ ion source, containing 1.8(7)% of 1s2s 3S1 metastable ions with an energy of ∼500 eV, is obtained by an electron bombardment process. The ion current can stay more than 250 h with the variation of ∼0.3%, and the divergence of ion beam is ∼0.5 mrad. The symmetric profile of Lamb dip signals of 1s2s 3S1--1s2p 3PJ transitions with linewidths of ∼50 MHz are obtained after subtracting Doppler background from the saturated fluorescence signals. A back-and-forth scan method is adopted to determine the FS/HFS splittings of 1s2p 3PJ states. Under these conditions, as a preliminary test, several splittings of 7Li+ are measured. The statistical uncertainties of the FS/HFS splittings are estimated to be less than 50 kHz, and the results are one order of magnitude better than previous results. The apparatus is feasible to precisely determine the splittings of energy levels of alkali and alkaline earth ions.

Pressure broadening of atomic oxygen two-photon absorption laser induced fluorescence

Atomic oxygen, considered to be a determining reactant in plasma applications at ambient pressure, is routinely detected by two-photon absorption laser induced fluorescence (TALIF). Here, pressure broadening of the (2p4 3P2 → 3p 3PJ=0,1,2) two-photon transition in oxygen atoms was investigated using a high-resolution TALIF technique in normal and Doppler-free configurations. The pressure broadening coefficients determined were = 0.40 ± 0.08 cm−1/bar for oxygen molecules and = 0.46 ± 0.03 cm−1/bar for helium atoms. These correspond to pressure broadening rate constants = 9 · 10–9 cm3 s−1 and = 4 · 10−9 cm3 s−1, respectively. The well-known quenching rate constants of O(3p 3PJ) by O2 and He are at least one order of magnitude smaller, which signifies that non-quenching collisions constitute the main line-broadening mechanism. In addition to providing new insights into collisional processes of oxygen atoms in electronically excited 3p 3PJ state, reported pressure broadening parameters are important for quantification of oxygen TALIF line profiles when both collisional and Doppler broadening mechanisms are important. Thus, the Doppler component (and hence the temperature of oxygen atoms) can be accurately determined from high resolution TALIF measurements in a broad range of conditions.

New insight into two-step near-infrared quantum cutting in Pr^3+ singly doped oxyfluoride glass-ceramics

Efficient near-infrared (NIR) quantum cutting (QC) in RE3+/Yb3+ requires the UV-blue photon excited RE3+ donor has intermediate energy level to separate the energy gaps (~10000 cm−1) resonant to Yb3+absorption. Thus the unique Pr3+/Yb3+ resonant QC at low Yb3+content (room temperature) essentially requires Pr3+-doping features distinctive NIR radiative transitions: in our prepared Pr3+-doped oxyfluoride glass-ceramics containing CaF2 nanocrystals, a two-photon NIR-QC from blue-photon excited 3Pj (j = 0, 1, 2) states takes place efficiently with 1G4 acting as an intermediate level. The underlying energy transfer mechanisms involving the two-step sequential transitions of 3P0→1G4 ~915 nm and 1G4→3H4 ~990 nm (crucial resonant routes for the further 1Pr3+→2Yb3+), as well as the 1D2→3F2 ~873 nm and 1D2→3F3,4 ~1040 nm, are rationally distinguished by means of photoemission, excitation, and time-resolved fluorescence spectra.

Population of 2p 54p levels of Ne in the afterglow of discharge in helium with small admixtrue of neon

The processes of population of 3p1, 3p3, 3p6, and 3p9 levels (in Paschen’s notation) of neon atom has been studied by spectroscopic methods during the decay period of plasma produced in helium containing small concentrations of neon ([Ne]/[He] ≈ 10–5). Based on the comparative analysis of temporal variation of the intensities of NeI spectral lines of 2p54p → 2p53s and 2p54d → 2p53p transitions, it is established that the formation of exited Ne(2p54p) atoms in the afterglow is related to the dissociative recombination (DR) of homo- and heteronuclear ions and electrons via reactions HeNe+ + e → Ne(2p54p) + Ne and Ne2+ e → Ne(2p54p) + Ne. The relative contributions of these processes to the rate of population of various Ne(3pj) states depend on the energies of 3pj levels. The upper 3p1 level lying above the ground state of Ne2+(v = 0) ion is populated almost entirely due to the DR of HeNe+ heteronuclear ions. The DR of Ne2+ ions and electrons significantly contributes to \(\Gamma _{3p_j }^{Ne_2^ + }\) flux in population of low-lying 3p3, 3p6, and 3p9 levels; \(\Gamma _{3p_j }^{Ne_2^ + }\) value increases with decreasing energy of 3pj level.

The effect of collisional quenching of the O 3p 3PJ state on the determination of the spatial distribution of the atomic oxygen density in an APPJ operating in ambient air by TALIF

The spatial profile of the absolute atomic oxygen density is obtained by two-photon absorption laser-induced fluorescence (TALIF) in an Ar+2% air cold atmospheric pressure plasma jet (APPJ) operating in ambient air. The varying air concentration in the jet effluent which contributes to the collisional quenching of the O 3p 3PJ state, pumped by the laser, strongly influences the recorded TALIF signal under the present experimental conditions. The spatially resolved air densities obtained from Raman scattering measurements have been reported in our previous work (van Gessel et al 2013 Appl. Phys. Lett. 103 064103). These densities allow us to calculate the spatially dependent collisional quenching rate for the O 3p 3PJ state and reconstruct the spatial O density profile from the recorded TALIF signal. Significant differences between the TALIF intensity profile and the actual O density profile for the investigated experimental conditions are found.

Luminescence of Pr$^{3+}$ Doped LuCl$_3$ and LuBr$_3$ Under Intraconfigurational $(4{\rm f}^2 \rightarrow 4{\rm f}^1 5{\rm d}^1)$ and Band Gap Excitation

The optical properties of Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> activated LuCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and LuBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> under intra-ionic 4f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> rarr 4f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> 5d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> and band gap (lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex</sub> = 193 nm; X-ray) excitations have been evaluated. The luminescence of Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> in these hosts is found to be strongly dependent on the excitation energy: for energies less than the absorption edge of the host, the luminescence is dominated by the 4f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> 5d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> rarr 4f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> interconfigurational optical transitions. When luminescence is excited by photons with energies corresponding to the absorption edge or the band gap of the host, the emission spectrum is dominated by the intraconfigurational 4f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> rarr 4f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> optical transitions, which emanate from the Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> P <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> states. A model to account for the dependence of the emission behavior of Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ion on the excitation energy is presented.

Luminescence of LuCl$_3$ Doped With Pr$^{3+}$

The optical properties of Pr3+ activated LuCl3 under intra-ionic 4f2 rarr 4f1 5d1 and band gap (lambdaex = 193 nm; X-ray) excitations has been evaluated. The luminescence of LuCl3 :Pr3+ is found to be strongly dependent on the excitation energy: for energies less than the absorption edge of the host, the luminescence of LuCl3: Pr3+ is dominated by the 4f1 5d1 rarr 4f2 interconfigurational optical transitions. When luminescence is excited by photons with energies corresponding to the absorption edge or the band gap of the host, the emission spectrum is dominated by the intraconfigurational 4f2 rarr 4f2 optical transitions, which emanate from the Pr3+ 3PJ states. The luminescence efficiency of the inter- and intraconfigurational optical transitions is high at room temperature. A model to account for the dependence of the emission behavior of Pr3+ ion on the excitation energy is presented.

Progress in helium fine-structure calculations and the fine-structure constant

The long-term goal of this work is to determine the fine-structure constant α from a comparison between theory and experiment for the fine-structure splittings of the helium 1s2p 3PJ states. All known terms of order α5 a.u. (α7 mc2) arising from the electron–electron interaction, and recoil corrections of order α4 µ / M a.u. are evaluated and added to previous tabulation. The predicted energy splittings are ν0,1 = 29 616.946 42(18) MHz and ν1,2 = 2291.154 62(31) MHz. Although the computational uncertainty is much less than ±1 kHz, there is an unexplained discrepancy between theory and experiment of 19.4(1.4) kHz for ν1,2. PACS Nos.: 31.30Jv, 32.10Fn

Precise theory of the Stark effect on hydrogen- and helium-like atoms

The relativistic effects on the dipole polarizabilities and hyperpolarizabilities are considered for different kinds of energy levels in hydrogen- and helium-like atoms. The relativistic Coulomb Green's function is used for calculating the susceptibilities of the ground-state hydrogen up to terms of order (α Z)10. Both relativistic and interelectronic corrections are determined for the ground state of helium. The formulas are given for polarizability and hyperpolarizability in the relativistic "screened-charge" approximation. The anticrossing of the triplet 3PJ states with zero magnetic quantum number is studied on the basis of perturbation theory for degenerate states. General expressions are given for the dipole matrix elements, up to the fourth order in field strength, within the basis of close fine-structure substates with equal angular momenta L and different total momenta J. The calculation of the higher order matrix elements is carried out with the use of the Green's function in the model potential approximation. PACS Nos.: 31.10Dk, 31.15Ar, 31.30Jv, 32.10-f, 31.25Eb

The complete mα6 contribution tothe helium 2 3PJ energy

A complete calculation of the mα6 contribution to the heliumionization energy of 2 3PJ states is presented. The result, beyondthe previously known radiative corrections, amounts to 0.4046 MHzand significantly reduces theoretical uncertainties.The computational method is based on the effective Hamiltonianderived from relativistic quantum electrodynamic theory.The current status of theoretical predictions is summarizedand a comparison with the latest experimental results isperformed.

Quenching of excited P11 state atomic zinc by molecular nitrogen: A matrix-isolation spectroscopy/quantum chemical calculation study

A concentration study is used to identify the optical absorption of zinc atoms isolated in solid nitrogen. Photoexcitation of the threefold-split, atomic 4p 1P1 singlet absorption band did not produce any emission from either the singlet or triplet states. Hartree–Fock (relativistic effective core potentials) plus variational and multireference perturbational configuration-interaction calculations are performed to analyze this very efficient quenching of excited state atomic zinc by molecular nitrogen. Of the two geometries considered in energy calculations of the approach of Zn(1P1) to N2, the collinear exhibited a slightly greater stabilization than the perpendicular approach. However, the collinear is identified as of no significance in the excited state quenching due to the absence of low energy crossings with the ground state. In contrast, for the perpendicular approach a crossing between the repulsive ground A11(1S0) state and the strongly attractive B12(1P1) state occurs close to the energy minimum of the B12 state. The efficiency of crossing between these states is analyzed in the framework of one-dimensional Landau–Zener (LZ) theory. A hopping probability of 0.07 is obtained for a single crossing, considered important in a rapidly relaxing solid state system, such as present in a low temperature matrix. Crossings found between the repulsive B31(3P1) and A31(3P1) states with the strongly bound B12(1P1) state are expected to play a role in gas phase Zn(1P1) quenching leading to the production of Zn(3PJ) states. LZ calculations indicate a small hopping probability for these crossings, consistent with the small P11→3PJ quenching cross sections observed in the gas phase work.

The J = 2 even-parity spectrum for high members of theSr I 5snd 1,3D2 Rydberg series in thepresence of electric fields and weak collisions

An experimental study of the two-photon spectra of high membersof the Sr I 5snd 1,3D2 Rydberg series isdescribed. We use transverse excitation of an atomic beam witha narrow-bandwidth tuneable dye laser within a heat pipeequipped for field ionization detection. The presence of weakcollisions has revealed several anomalies. Strong spin-orbitinteraction and the breakdown of parity and selection rulescombined with `l' mixing are observed. The breakdown is dueto the Stark field present in the interaction region.Single-photon transitions originating from the5snp 1P1 and 5snp3PJ statespopulated by electron impact excitations are also observed.They create highly compact doubly excited 4d23PJ, 5p21D2 and4d5p 3PJ states, which act as dominant intruders inthe observed spectrum. Such states with highly localizedorbitals survive collision and field effects, whereas Rydbergstates are highly sensitive to external perturbations. Also, wehave observed l-changing collisional processes like Ar + Sr (5s}nd 1,3D2) → Sr (5snl,l⩾ 3).Several members of a new series which begin to appear at largen are observed and are tentatively designated as the5snf 1F3 Rydberg series. Furthermore, we haveobserved and identified several members of the Sr I5snp 1P1 and 5snp 3P2 Rydbergseries by two-photon absorption from the ground state. They areexcited via the breakdown of parity and other selection rules,owing to the presence of external fields. New values of energylevels of the Sr I 5snd 1,3D2 Rydberg series arepresented: n=25-73 for singlet and n=25-47 for tripletmembers, obtained from two-photon spectra. Comparison of thesevalues with those given by other authors who used differentexcitation schemes shows good agreement. The spectrum offluorescence emission from a low-pressure discharge around thefield ionization probe was obtained using amonochromator-photomultiplier detection system. The emissionlines confirm the collisional excitations observed in thespectra of the Rydberg series. An energy level diagramsummarizing the various transitions observed in our study isalso presented.

A Search for Isotope Effects in Chemiluminescent Reactions of Metastable Ca*( 3Pj, 1D2 ) Atoms with CH3I and CD3I Molecules

Chemiluminescent reactions of calcium atoms in the metastable 3Pj and 1D2 states with CH3I and CD3I were studied in a beam-gas arrangement. Calcium monoiodide spectra associated with transitions from the electronic A 2Π, B 2Σ+ and C 2Π states to the X 2Σ+ ground state were recorded. Total collision and chemiluminescence cross sections were measured. It was found that isotopic substitution in the methyl group does not change the reaction cross sections and the chemiluminescence spectra.

COLLISIONAL ENERGY POOLING BETWEEN EXCITED SODIUM ATOMS

The collisional energy pooling process in a sodium vapor [ Na(3PJ)+Na(3PJ′)→Na(nLJ″)+Na(3S1/2)] is experimentally investigated. At sufficiently low sodium densities,such that only the optically excited 3PJ state is significantly populated, the ratios of nLJ″ fluorescence intensities and the relative density of Na(3P1/2) versus the density of Na(3P3/2) are measured. The ratios of rate coefficients k(nLJ′)(J, J′) relative to k5S(3/2,3/2) are given for nLJ″= 4D3/2, 4D5/2, 4F5/2, 4F7/2, and 5S1/2, each for J = J′ =1/2 and 3/2. At high sodium densities, the 3P states are populated in nearly statistical ratios, the ratios of the k(nLJ″)(1/2,3/2) relative to k5S(3/2,3/2) are obtained.

General methods for evaluating matrix elements of singular operators in two-electron systems

Due to the recent advances in both theory and experiment for the fine structure of two-electron atomic systems, it is necessary to include quantum electrodynamic (QED) effects through orders α6mc2, α7ln(Zα)mc2, and α7mc2, in order to match the experimental precision. These effects can be expressed in terms of a sum of singular operators. A general scheme is given for the evaluation of a wide range of matrix elements of high-order singular QED operators for two-electron atomic systems in Hylleraas coordinates. The scheme presented here can be applied to triplet states with arbitrary angular momentum. A number of useful expressions for the analytical evaluation of radial integrals are derived. An example is given in calculating the Douglas and Kroll terms, and the numerical values of the reduced matrix elements are presented for the 2 3PJ states of helium.

Collisional processes of laser excited Ca with noble gases

We report an investigation of collisional processes in Ca vapour in the presence of noble gases under 1S0 to 1P1 laser excitation. We observe the process of energy transfer to the triplet 3PJ(J=1, 3) states and the process of energy pooling to many higher energy states. The combination of these processes makes it possible, by changing pressure and kind of noble gas, to 'drive' the population distribution of the upper states.

II-VI compound thin-film deposition by resonant laser sputtering

Time-resolved laser-induced fluorescence measurements indicate that Zn atoms excited to the 4 3PJ metastable state react rapidly with group-VI molecules O2, CS2, and H2S. Rate constants for these processes are presented. Based on these data, a method for deposition of thin films of the ZnO or ZnS products of these reactions is demonstrated, wherein the Zn atoms are both sputtered from a target and excited to the 4 3PJ state by near-resonant radiation from a pulsed XeCl laser.