3P Atoms Research Articles

First-principles study on the electronic structure and optical properties of Tl2Cd2(SO4)3and Rb2Cd2(SO4)3

With the help of ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculating the electronic structure and linear optical properties is carried out for XCd2(SO4)3 (X =Tl, Rb). The results show that Tl2Cd2(SO4)3 (TlCdS) has a larger band gap than Rb2Cd2(SO4)3 (RbCdS) and the energy bands for RbCdS are more dispersive than those of TlCdS. From their partial densities of states (PDOS), we have observed that the hybridization between S ionic 2p and O atomic 2p orbitals forms SO4 ionic groups. The remarkable difference between RbCdS and TlCdS is, however, the degree of hybridization between cation (Tl and Rb) and its surrounding oxygen atoms. In the view of quantum chemistry, the strong p-d hybridization indicates the existence of their cation ionic bonds (Cd-O, Rb-O, and Tl-O). The calculations of TlCdS and RbCdS show their optical properties to be less anisotropic. Their anisotropies in the optical properties mainly occur in a low photon energy region of 5-16 eV.

Ab Initio Treatment of the Chemical Reaction Precursor Complex Br(2P)−HCN. 2. Bound-State Calculations and Infrared Spectra

Rovibronic energy levels and properties of the Br(2P)-HCN complex were obtained from three-dimensional calculations, with HCN kept linear and the CN bond frozen. All diabatic states that correlate to the 2P3/2 and 2P1/2 states of the Br atom were included and spin-orbit coupling was taken into account. The 3 x 3 matrix of diabatic potential surfaces was taken from the preceding paper (paper 1). In agreement with experiment, we found two linear isomers, Br-NCH and Br-HCN. The calculated binding energies are very similar: D0 = 352.4 cm(-1) and D0 = 349.1 cm(-1), respectively. We established, also in agreement with experiment, that the ground electronic state of Br-NCH has |Omega| = (1/2) and that Br-HCN has a ground state with |Omega| = (3/2), where the quantum number, Omega, is the projection of the total angular momentum, J, of the complex on the intermolecular axis R. This picture can be understood as being caused by the electrostatic interaction between the quadrupole of the Br(2P) atom and the dipole of HCN, combined with the very strong spin-orbit coupling in Br. We predicted the frequencies of the van der Waals modes of both isomers and found a direct Renner-Teller splitting of the bend mode in Br-HCN and a smaller, indirect, splitting in Br-NCH. The red shift of the CH stretch frequency in the complex, relative to free HCN, was calculated to be 1.98 cm(-1) for Br-NCH and 23.11 cm(-1) for Br-HCN, in good agreement with the values measured in helium nanodroplets. Finally, with the use of the same potential surfaces, we modeled the Cl(2P)-HCN complex and found that the experimentally observed linear Cl-NCH isomer is considerably more stable than the (not observed) Cl-HCN isomer. This was explained mainly as an effect of the substantially smaller spin-orbit coupling in Cl, relative to Br.

On the ground and some low-lying excited states of ScB: A multiconfigurational study

The electronic structure of a series of low-lying excited triplet and quintet states of scandium boride (ScB) was examined using multireference configuration interaction (including Davidson's correction for quadruple excitations) and single-reference coupled cluster (CC) methods with averaged natural orbital (ANO) basis sets. The CC approach was used only for the lowest quintet state. The authors have analyzed eight low-lying triplets 3Sigma-(2), 3Sigma+, 3Pi(3), and 3Delta(2) dissociating to Sc(2D)/B(2P) atoms and eight low-lying quintet states 5Sigma-, 5Sigma+, 5Pi(2), 5Phi, and 5Delta(3) dissociating to Sc(4F)/B(2P) atoms. They report the potential energy curves and spectroscopic parameters of ScB obtained with the multireference configuration interaction (MRCI) technique including all singly and doubly excited configurations obtained with the ANO-S basis set. For the two lowest states they obtained also improved ANO-L spectroscopic constants, dipole and quadrupole moments as well as scalar relativistic effects based on the Douglas-Kroll-Hess Hamiltonian. They provide the analysis of the bonding based on Mulliken populations and occupation numbers. Since the two lowest states, 3Sigma- and 5Sigma-, lie energetically very close, their principal goal was to resolve the nature of the ground state of ScB. Their nonrelativistic MRCI(Q) (including Davidson correction) results indicate that the quintet is more stable than the triplet by about 800 cm(-1). Inclusion of scalar relativistic effects reduces this difference to about 240 cm(-1). The dissociation energies for 5Sigma- ScB range from 3.20 to 3.30 eV while those for the 3Sigma- range from 1.70 to 1.80 eV.

Influence of sustaining frequency on the production efficiency of excited Xe atoms studied in unit cell microplasma for ACPDPs using spectroscopic diagnostics

Abstract— The effects of the driving frequency of the sustaining‐voltage pulses on microplasmas in a cell of an ac plasma‐display panel (ACPDP) were investigated using spectroscopic diagnostics [optical emission spectroscopy (OES) and laser‐absorption spectroscopy (LAS)]. The unit discharge cell has a structure similar to that of a general commercial ACPDP, but it is prepared for three‐dimensional (3‐D) observation using a pair of micro‐prisms. When the near‐IR emission by OES and the absorption signal by LAS were observed in the front and side views simultaneously, it was determined that the discharge was concentrated at the center of the discharge space and quickly responded to an applied electrical potential as the sustaining frequency increases. The production efficiency of excited Xe**(2p) atoms and vacuum‐ultraviolet (VUV) photons, which was estimated from the spectroscopy results with the measured power dissipated in the discharges, increased as the frequency of the sustain pulses increases to 100 kHz. At 250 kHz, however, the efficiency remarkably decreased because of an inefficient time for excimer formation and, possibly, for wall‐charge formation. From the quantitative analysis of the efficiency, the most‐efficient frequency for the sustain voltage was around 100 kHz in the case of Xe(5%)‐Ne at 500 Torr, i.e., the efficiency depended on both the priming particles [excited Xe*(1s5) atoms] in space and the charged particles on the dielectrics.

Nitrogen pink afterglow: the mystery continues

This work extends our previous analysis of the nitrogen pink afterglow, by comparing our model predictions with the recently reported measurements of metastable N(2P) atoms and N2(a 1Πg) molecules. It is shown that both species reveal the presence of a characteristic maximum on their populations, occurring downstream from the discharge after an initial stage of decrease. Such behavior is a consequence of the V-V pumping-up mechanism taking place during the relaxation in the afterglow, which is followed by V-E transfers that create locally N2(A 3Σ+u) and N2(a′ 1Σ−u) metastables. The model predictions significantly overestimate the density of the N2(a 1Πg) state, revealing a problem in the description of the singlet kinetics. As singlet N2(a′ 1Σ−u) metastables play a crucial role in nitrogen ionization, the new results imply that the ionization mechanisms in the afterglow may have to be reviewed.

Radiation trapping in LiF ablation plumes

This work highlights a potential pitfall associated with using optical emission to estimate the expansion velocity of material in laser ablation plumes, speci.cally when the monitored emission involves transition to a state that is present in high number density. Comparisons of time-gated, spatially resolved, images of the Li(3d. 2p) and Li(2p. 2s) emissions arising in the nanosecond 248 nm pulsed laser ablation of LiF enabled estimation of the distribution of ground state Li atoms in the plume. Analysis of these images revealed that the density of Li(2p) atoms in the early stages of the plume expansion was su.ciently high that even the Li(3d → 2p) emission profiles show evidence of radiation trapping.

Determination of Spin−Orbit Branching Fractions in the Photodissociation of Halogenated Hydrocarbons

Two methods based on vacuum ultraviolet (vuv) photoionization are presented for the determination of the spin-orbit branching fractions of the halogen atom produced in the photodissociation of halogenated hydrocarbons. Both methods make use of differences in the photoionization cross sections of the 2P(3/2) ground state and the 2P(1/2) excited-state of the neutral halogen atom. In the first approach, measurements of the total photoionization signal of the halogen atom are made at several vuv wavelengths, and the difference in the wavelength dependences for the 2P(3/2) and 2P(1/2) atoms allows the extraction of the branching fractions. In the second approach, the vuv wavelength is set close to the ionization threshold of the 2P(3/2) atom (well above that of the 2P(1/2) atom), and measurements are made at several electric field strengths, which shift the ionization threshold and thus vary the photoionization cross sections. In both methods, the relative cross sections of the ground- and excited-state atoms are determined by using the known branching fractions for the 266 nm photodissociation of methyl iodide. These methods are applied to the photodissociation of isopropyl iodide and allyl iodide, two systems for which standard ion-imaging techniques do not provide unique branching fractions.

Theoretical study on the angular correlation of two Lyman-α photons generated by single-photon absorption of a hydrogen molecule

The angular correlation of two Lyman-α photons generated by the linearly polarized single-photon absorption of H2(X 1Σg+) followed by the neutral dissociation of the doubly excited Q21Πu(1) state has been theoretically investigated with the second-order correlation function in quantum optics. A strong angular correlation has been obtained even for the molecules randomly oriented in space, due to the complicated entanglement of two H(2p) atoms in the intermediate state. It has been revealed how the symmetry properties in the electronic state are transferred to the two-photon state and how they manifest themselves in the angular correlation function.

The influence of correlation on the interpretation of Hund’s multiplicity rule: A quantum Monte Carlo study

A systematic quantum Monte Carlo study of 2p atoms (C, N, O) and 3p atoms (Si, P, S) is performed to investigate the influence of correlation on the interpretation of Hund's multiplicity rule, which is an extension of our previous study of the carbon atom [J. Chem. Phys. 121, 7144 (2004)] to heavier atoms. The accuracy in the present study is significantly improved as compared with the previous study. A detailed analysis of the correlation contribution to individual energy components of the total energy is given beyond the self-consistent Hartree-Fock calculation. The stability of the highest spin-multiplicity state of all the atoms is ascribed to the greater electron-nucleus attraction energy that is gained at the cost of increasing the electron-electron repulsion energy as well as the kinetic energy. The present study demonstrates that correlation does not change the above conclusion due to the Hartree-Fock theory to support Boyd's less screening mechanism.

Photodissociation of Cyclobutyl Bromide at 234 nm Studied Using Velocity Map Imaging

This study investigates the 234 nm photodissociation dynamics of cyclobutyl bromide using a two-dimensional photofragment velocity imaging technique. The spin-orbit ground- and excited-state Br(2P) atoms are state-selectively detected via [2+1] resonance enhanced multiphoton ionization (REMPI), whereas the cyclobutyl radicals are ionized using 157 nm laser light. The Br(2P(3/2)) and the Br(2P(1/2)) atoms and their c-C4H7 radical cofragments evidence a single-peaked, Gaussian-shaped translational energy distribution ranging from approximately 14 to approximately 39 kcal/mol and angular distributions with significant parallel character. The Br(2P(1/2))/ Br(2P(3/2)) spin-orbit branching ratio is determined to be 0.11 +/- 0.07 by momentum match between the Br(2P) photofragments and the recoiling c-C4H7 fragments, assuming a uniform photoionization probability of the c-C4H7 radicals with an internal energy range of 10-35 kcal/mol. The REMPI line strength ratio for the detection of Br(2P(3/2)) and Br(2P(1/2)) atoms at 233.681 and 234.021 nm, respectively, is therefore derived to be 0.10 +/- 0.07. The measured recoil kinetic energies of the c-C4H7 radicals, and the resulting distribution of internal energies, indicates some of the radicals are formed with total internal energies above the barrier to isomerization and subsequent dissociation, but our analysis indicates they may be stable due to the substantial fraction of the internal energy which is partitioned to rotational energy of the radicals.

Band structures of TiO2 doped with N, C and B

This study on the band structures and charge densities of nitrogen (N)-, carbon (C)- and boron (B)-doped titanium dioxide (TiO(2)) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of impurity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of impurity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result. Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.

Interactions of 2P Atoms with Closed-Shell Diatomic Molecules: Alternative Diabatic Representations for the Electronic Anisotropy

The matrices of electrostatic and spin-orbit Hamiltonians for the system of a 2P atom interacting with a closed shell diatomic molecule in uncoupled, coupled, and complex-valued representations for electronic diabatic basis functions are rederived, and the unitary transformations connecting them are given explicitly. The links to previous derivations are established and existing inconsistencies are identified and eliminated. It is proven that the block-diagonalization of a 6 x 6 matrix of the electronic Hamiltonian is a result of using the basis functions with well-defined properties with respect to time reversal. Consideration of time-reversal symmetry also enforces phase consistency relevant for applications to multisurface reactive scattering and photodetachment spectroscopy calculations, as well as for perspective studies of inelastic effects in cold and ultracold environments. These and further developments are briefly sketched.

Ab Initio Treatment of the Chemical Reaction Precursor Complex Cl(2P)−HF. 1. Three-Dimensional Diabatic Potential Energy Surfaces

The three adiabatic potential surfaces of the Cl(2P)-HF complex that correlate with the 2P ground state of the Cl atom were calculated with the ab initio RCCSD(T) method (partially spin-restricted coupled cluster theory including single and double excitations and perturbative correction for the triples). With the aid of a geometry-dependent diabatic mixing angle, calculated by the complete active space self-consistent field (CASSCF) and multireference configuration-interaction (MRCI) methods, these adiabatic potential surfaces were converted to a set of four distinct diabatic potential surfaces required to define the full 3 x 3 matrix of diabatic potentials. Each of these diabatic potential surfaces was expanded in terms of the appropriate spherical harmonics in the angle theta between the HF bond axis r and the Cl-HF intermolecular axis R. The dependence of the expansion coefficients on the Cl-HF distance R and the HF bond length r(HF) was fit to an analytic form. The strongest binding occurs for the hydrogen-bonded linear Cl-HF geometry, with D(e) = 676.5 cm(-1) and R(e) = 6.217 a0 when r(HF) = r(e) = 1.7328 a0. This binding energy D(e) depends strongly on r(HF), with larger r(HF) causing stronger binding. An important contribution to the binding energy is provided by the interaction between the quadrupole moment of the Cl(2P) atom and the dipole of HF. In agreement with this electrostatic picture, the ground state of linear Cl-HF is a 2-fold degenerate electronic Pi state. For the linear Cl-FH geometry the states are in opposite order, i.e., the Sigma state is lower in energy than the Pi state. The following paper in this issue describes full three-dimensional computations of the bound states of the Cl-HF complex, based on the ab initio diabatic potentials of this paper.

Radiation trapping of the Hg 254 nm resonance line

The decay rate of Hg 6 3P1 atoms, due primarily to the escape of trapped 254 nm resonance radiation, was measured as a function of both Hg and Ar density in cylindrical, sealed fused silica cells. Time-resolved laser-induced fluorescence at 254 nm was used to obtain the decay rates for Hg densities from 5 × 1013 to 7 × 1015 cm−3 (22–101°C cold spot temperatures) and Ar densities from 0 to 9.7 × 1017 cm−3 in a cell of inner radius 1.05 cm. These new experimental data are compared to Monte Carlo results from a highly realistic code for simulating radiation trapping. This code includes Voigt profiles from a combination of Doppler, resonance, buffer gas and radiative line broadening, as well as hyperfine and isotopic structure with proper collisional redistribution. Upper limits on the rate constants for the quenching of Hg 6 3 P1 atoms by collisions with ground level Ar and Hg atoms were derived. Additional Monte Carlo simulations covering cell radii from 0.1 to 3.0 cm were performed. A broadly applicable engineering formula is derived from this study, which predicts the Hg 6 3P1 decay rate from 254 nm resonance radiation trapping as a function of Hg and Ar densities and cell radius.

Direct Excitation of H(2P) Atoms due to Collisions with Protons and Antiprotons

Excitation of hydrogen atoms, being initially in the excited 2p state by colliding with protons (p) and antiprotons (p) is investigated within the impact parameter method. The calculation involves the n = 1,2,3,4 states of the target in addition to considers previously, in an incident energy range from 3 keV to 1000 keV. The effect of the electric charge of the projectile on the collision is discussed.

Orbital Hybridization of the Ferroelectric Rb2Cd2(SO4)3: Origin of Domain Walls

We perform first-principle calculations for the study of theorthorhombic Rb2Cd2 (SO4)3 structure. Electronic energy bands,total and partial densities of states are reported and analysed. It isfound that oxygen atomic 2p electrons strongly hybridize with Rb/orCd 4d and S 2p states, resulting in two-type ionic groups with weakcouplings. It is shown that macroscopic domain walls originate fromsuch weak-coupling ionic groups, arising at the cell boundaries. Theasymmetric cation bonds (Rb–O and Cd–O) and the subsequent rotations ofthe SO4 tetrahedra can lead to the driving force of the ferroelectricbehaviour. The predicted pyroelectric current effects are observedexperimentally in the ferroelectric phase.

Kinetic energy distributions and line profile measurements of dissociation products of water upon electron impact

The Doppler line profiles of H Ly‐α (1216 Å) and O I (1302 Å and 1152 Å) resulting from electron impact dissociative excitation of H2O have been measured with a high‐resolution (λ/Δλ = 50,000) ultraviolet spectrometer. The line profiles are used to calculate the kinetic energy distribution of the hydrogen atoms produced in dissociative excitation and ionization of H2O at electron impact energies 25, 35, and 100 eV. Three distinct populations of H(2p) atoms were found. The kinetic energy of hydrogen atoms is found to have contributions from a low‐energy component, with a mean energy of ∼0.2 eV at all the three electron impact energies. In addition, a medium‐energy component appears with a mean energy of ∼2.0 eV for 35 eV electrons, and a high‐energy component, ∼7 eV, for 100 eV electrons. The measurement of O I (1302 Å) and O I (1152 Å) line profiles indicate that the kinetic energy of excited O I atoms is very small (∼1 eV or less) at all electron impact energies. Most of the energy released in dissociation is found in the translational energy of the hydrogen atoms. The excitation functions of H Ly‐α, O I (1302 Å) feature of oxygen, and A(0) − X(0) molecular band of hydroxyl near 3050 Å from threshold to 600 V were also measured. The spectrum (1.0 Å FWHM) of the rotational structure of OH (A − X) from electron impact dissociation indicates a high degree of rotational excitation, which is almost identical to the rotational structure from dissociative recombination of H2O+. The results presented in this paper have important applications to planetary bodies, like comets, icy satellites of outer planets, Saturn's magnetosphere, and rings, all of which have H2O and its daughter products in large amount.

X-ray absorption spectra for transition metal high-κ dielectrics: Final state differences for intra- and inter-atomic transitions

This article applies x-ray absorption spectroscopy to a study of the electronic structure of the high-k gate dielectrics, TiO2, ZrO2, and HfO2. Qualitative and quantitative differences are identified between intra-atomic transitions such as the Zr 3p-state, M2,3 core state absorptions which terminate in TM 4d*- and 5s*-states, and inter-atomic transitions such as the Zr 1s- and O 1s-state K1 absorptions which terminate in Zr 4d*- and 5s*-states that are mixed with O atom 2p* states through nearest neighbor bonding interactions. Differences between the spectral peak energies of the lowest d*-features in the O K1 spectra are demonstrated to scale with optical band gap differences for TiO2, ZrO2, and HfO2, providing important information relevant to applications of TM oxides as high-κ gate dielectrics in advanced Si devices. This is demonstrated through additional scaling relationships between (i) conduction band offset energies between Si and the respective dielectrics, and the optical band gaps, and (ii) the conduction band offset energies, and the electron tunneling masses as well.

2p Photoelectron spectroscopy of the late 3d transition metal atoms

Employing electron spectrometry in conjunction with third generation synchrotron radiation (SR), we present a short overview of the 2p photoelectron spectroscopy of free 3d transition metal atoms. In particular, this paper will focus on the late transition metals from Cr to Cu and a comparison of the free atoms to several compound systems. The atomic experimental spectra are compared to theoretical spectra based on Hartree-Fock (HF) and configuration interaction (CI) calculations. In general a good agreement between experiment and theory is found already for single configuration HF calculations and the observed satellites in the atomic 2p photoelectron spectra (PES) can be attributed to a recoupled 3d valence shell. However, for Ni mixing of several configurations in the final state have to be taken into account.

Ab initio study of the reactions of Ga(2P, 2S, and 2P) with methane.

The interactions of Ga(2P:4s(2)4p1, 2S:4s(2)5s1, and 2P:4s(2)5p1) with CH4 is studied by means of Hartree-Fock self-consistent-field (SCF) calculations using relativistic effective core potentials and multiconfigurational-SCF plus multireference variational and perturbational on second-order Möller-Plesset configuration interaction calculations. The Ga atom 2P(4s(2)5p1) state can spontaneously insert into the CH4. In this interaction the 4 2A potential energy surface is initially attractive and becomes repulsive only after meeting with the 3 2A surface, adiabatically linked with the Ga(2S:4s(2)5s1) + CH4 fragments. The Ga atom 2S(4s(2)5s1) excited state inserts in the C-H bond. In this interaction the 3 2A potential energy surface initially attractive, becomes repulsive after meet the 2 2A' surface linked with the Ga(2P:4s(2)4p1) + CH4 fragments. The two 2A curves (2 2A and X 2A) derived from the interaction of Ga(2P:4s(2)4p1) atoms with methane molecules are initially repulsive. The 2 2A curve after an avoided crossing with the 3 2A curve goes smoothly down and reaches a minimum: after this point, it shows an energy barrier. The top of this barrier is located below the energy value of the Ga(2S:4s(2)5s1) + CH4 fragments. After this energy top the 2 2A curve goes down to meet the X 2A curve. The 2 2A curve becomes repulsive after the avoided crossing with the X 2A curve. The X 2A curve becomes attractive only after its avoided crossing with the 2 2A curve. The lowest-lying X 2A potential leads to the HGaCH3 X 2A intermediate molecule. This intermediate molecule, diabatically correlated with the Ga(2S:4s(2)5s1) + CH4 fragments, which lie 6 kcal/mol, above the ground-state reactants, the dissociation channels of this intermediate molecule leading to the GaH + CH3 and H + GaCH3 products. These products are reached from the HGaCH3 intermediate without activation barriers. The work results suggest that Ga atom in the first excited state in gas-phase methane molecules could produce better quality a-C:H thin films through CH3 radicals, as well as gallium carbide materials.