Quantum Defect Orbital Method Research Articles

MRSDCI Vertical Excitation Energies and MQDO Intensities for Electronic Transitions to Rydberg States in H2S

Vertical excitation energies and the ionization potential for H2S have been calculated through the multireference singles and doubles configuration interaction method. We have used these values to calculate oscillator strengths of H2S. The molecular quantum defect orbital method has been employed to determine analytical wave functions and transition intensities involving Rydberg states. The results have been analyzed on the grounds of the data available in the literature.

Ground and excited states of NH4: Electron propagator and quantum defect analysis.

Vertical excitation energies of the Rydberg radical NH4 are inferred from ab initio electron propagator calculations on the electron affinities of NH4+. The adiabatic ionization energy of NH4 is evaluated with coupled-cluster calculations. These predictions provide optimal parameters for the molecular-adapted quantum defect orbital method, which is used to determine Einstein emission coefficients and radiative lifetimes. Comparisons with spectroscopic data and previous calculations are discussed.

Theoretical study of the valence and K‐shell spectra of atmospherically relevant CO2

AbstractCalculations of intensities for E1 electronic transitions originating in the nonbonding orbitals of CO2 and ending in low‐Rydberg states, as well as the corresponding partial‐channel and total photoionization density of oscillator strength, have been performed with the molecular quantum defect orbital (MQDO) method. This article thus deals with both the nonbonding orbitals constituent of the outer valence shell and the atomic‐like K‐shell of CO2. A comparative analysis is made throughout the discrete and continuous spectral regions with the results of previously reported experimental and theoretical studies for this species. Good agreement is found in most cases. The MQDO approach in this and in previous applications to molecular Rydberg states has proved to yield results of quantitative quality as long as the involved states are not subject to strong perturbations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Rydberg Series as Ionization Channels: Photoabsorption and Photoionization of the Atmospherically Relevant Molecule NO

The photoionization of nitric oxide from its ground state has been studied with the molecular-adapted quantum defect orbital (MQDO) method. Partial differential oscillator strengths for the different Rydberg series that constitute the ionization channels of NO from its ground state have been calculated up to a photon energy of 60 eV. The continuity of the calculated differential oscillator strengths across the ionization threshold, that is, in the discrete and continuous regions of the spectrum, has been adopted as a quality criterion, given the scarcity of comparative data.

Trends in E2 and M1 transition rates between 3p${_{{\mathsf{3/2}}}}$ and 3p${_{\mathsf{{1/2}}}}$ levels in 3s${^{\mathsf{2}}}$ 3p${^k}$ systems

The analysis of forbidden lines, such as E2 and M1, in the atomic spectra emitted by certain ions is important for the study of the plasma in astrophysical objects and fusion devices. Transition rates between 3p 3 / 2 and3p 1 / 2 levels in 3s 2 3p k ions that belong to the aluminium sequence have been calculated with the Relativistic Quantum Defect Orbital (RQDO) method. The present data are tested by comparison with other theoretical data available in the literature, and the regularity of the transition intensities along the isoelectronic sequence for both (E2 and Ml) lines, as well as their competition, are also analysed.

Intensity calculations of the VUV and UV photoabsorption and photoionisation of CF 3Cl

Absorption oscillator strengths and photoionisation cross-sections for CF 3Cl from its ground state are reported. The molecular-adapted Quantum Defect Orbital (MQDO) method has been employed in the calculations. Partial differential oscillator strengths for the different Rydberg series that constitute the ionisation channels of CF 3Cl, as well as the photoionisation cross-sections, from its ground state are reported. The calculated cross-sections conform fairly well with experimental and theoretical values found in the literature.

Spectroscopy of forbidden transitions in ions of astrophysical interest

The spectroscopic study of forbidden transitions in ions of astrophysical interest has been performed using an extension of the well-established relativistic quantum defect orbital (RQDO) method. The method has so far proved to be a very useful tool for predicting a large body of electron transition probabilities, and other related properties. The RQDO method has been applied to the study of E2 transitions in the spectra of ions relevant in astrophysics, such as Ti XII, Fe XVI, Co XVII and Ni XVIII.

MCDF and RQDO study of the fine-structure lines of transition arraynp$^2 \to n$p $(n+1)$s in isoelectronic atomic systems

Relativistic calculations of electric dipole (E1) allowed transition for a number of ions in the germanium sequence have been performed. Oscillator strengths for fine-structure transitions within the 4p 2 -4p5s array have been calculated with both the Multiconfigurational Dirac-Fock (MCDF) approach and the Relativistic Quantum Defect Orbital (RQDO) method. The results are analysed on the grounds of the theoretical data available in the literature. Also, a comparative analysis with the homologous silicon sequence is made. The spectra of systems such as Mo XI are important in the context of plasma physics and thermonuclear fusion measurements.

Relativisticeffects and systematic trends in electric quadrupole transition probabilitiesfor Na-like ions

Transition probabilities for electric quadrupole (E2) spectral lines between levelswith Δl = 0 of the Na isoelectronic sequence, fromSi IV (Z = 14) to Kr XXVI (Z = 36), have been calculated inthe LSJ-coupling scheme using the relativistic quantum defectorbital method. Our data are compared with the very fewresults available, and their systematic trends as well as theinfluence of the main relativistic contributions to theoscillator strengths are analysed for several transitions alongthis sequence.

Intensities of Vibronic Transitions for the Main Bands Observed in the Electronic Spectrum of Atmospherically Relevant Nitric Oxide

Absorption oscillator strengths for the γ(A2Σ+−X2Π), δ(C2Π−X2Π), and ε(D2Σ+−X2Π) bands of NO, which are relevant to the study of atmospheric processes are reported. We have calculated both electronic and vibronic transition probabilities with the molecular-adapted quantum defect orbital (MQDO) method, which has proved, in previous applications, to be an adequate theoretical tool in the context of Rydberg spectra. The results appear to be in good accord with the available experimental values and, with some exceptions, conform fairly well with theoretical data derived from rather more sophisticated methods.

Study of Rydberg transitions in NaHe

Einstein coefficients and oscillator strengths for electronic transitions in the Rydberg radical NaHe have been calculated with the molecular-adapted quantum defect orbital (MQDO) method. The correctness of our estimations has been established on the basis of their good agreement with the results of a reliable complex calculation available in the literature. Transition probability data involving Rydberg states lying higher in energy than those so far reported are supplied.

Photoabsorption of Nitrous Oxide through Rydberg States in the Bound and Continuum Spectral Regions: Main Ionization Channels

The oscillator strength spectral density for the partial (through different individual Rydberg series) and total photoabsorption processes which determine the photoionization of N2O from its ground state has been studied. Despite its relevance for atmospheric chemistry and astrochemistry, only a few data seem to be available in the literature. The molecular-adapted quantum defect orbital (MQDO) method has been employed in the calculations. For the different ionization channels, continuity between the bound and continuum spectral regions has been achieved in the corresponding partial differential oscillator strengths. Good agreement with experiment has been found for the total photoionization cross section.

Theoretical study of the Rydberg spectra of chemically relevant isovalent radicals

AbstractIn the present work we have studied the Rydberg spectroscopic behavior of the CH3 and SiH3 isovalent radicals. The molecular‐adapted quantum defect orbital (MQDO) method has been employed in our calculations, which have been extended to the radicals' isolated central atoms, C and Si. The similarities observed between the intensities of analogous transitions in the atoms and the corresponding radicals have not only served the purpose of assessing the quality of our calculations but also offer some potential practical usefulness. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

Systematic trends in E2 transitions along the sodium isoelectronic sequence

AbstractOscillator strengths for E2‐forbidden spectral lines of sodium‐isoelectronic ions, from K IX (Z=19) to Cs XLV (Z=55), have been calculated in the LS‐coupling scheme using the relativistic quantum defect orbital (RQDO) method. The study of many of these sodiumlike ions is relevant to processes in fusion devices and in astrophysical objects. Our data are compared with the very few results available, and their systematic trend is analyzed for np 2P0–n′f 2F0 transitions. The influence of relativistic effects in E2 transitions along this sequence is also discussed. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

Excitation Energies and Molecular Quantum Defect Orbital Transition Intensities for Rydberg States of ArH

The size-consistent self-consistent complete active space singles and doubles configuration interaction ((SC)2-CAS-SDCI) procedure has been applied to the calculation of vertical excitation energies, as well as the ionization energy, of the Rydberg radical ArH. Absorption oscillator strengths and Einstein emission coefficients for a number of electronic transitions have been obtained with the molecular adapted quantum defect orbital (MQDO) method. The adequacy of the two theoretical procedures employed in the present work is discussed.

Relativistic quantum defect orbital study of forbidden transitions in Co16+

Theoretical line strengths and transition probabilities for electric quadrupole (E2) transitions between levels belonging to several important configurations of Co 16+ are reported. The calculations have been carried out with the Relativistic Quantum Defect Orbital (RQDO) method. A general good accord between the present results and some earlier theoretical data is found. Some of the E2 transition probabilities are reported for the first time. The correct systematic behaviour of the RQDO line strengths along the spectral series is reproduced by the present results in the absence of configuration mixing. This semiempirical method appears to adequately describe E2 transitions in this medium- Z atomic system.

Regularities along spectral series in forbidden transitions of Ti$\mathsf{^{11+}}$

Electric quadrupole (E2) transitions of Ti 11+ have been computed with the Relativistic Quantum Defect Orbital (RQDO) method. The correctness of our predictions has been analysed through the inspection of the systematic behaviour of the RQDO line strengths along the spectral series, and by the excellent accord of the SRQDO results with the scarce data available in the literature. Ti 11+ being one of the ions of the iron group, the study of its forbidden lines is of particular interest. The spectrum of this ion is important for the study of plasmas in astrophysical objects and fusion devices.

Photoabsorption processes in nitrous oxide and formaldehyde

AbstractAbsorption oscillator strengths and photoionization cross sections for electronic transitions involving Rydberg states that are relevant to the photochemistry of N2O and H2CO are reported. These compounds have been found to play an important role in the evolution of Earth's upper atmosphere. However, the difficulties encoutered in both laboratory measurements and theoretical calculations on the photoabsorption of these compounds are responsible for the scarcity of data in the literature. The present calculations have been performed with the molecular‐adapted quantum defect orbital (MQDO) method, of which the adequacy for this type of studies has recently been assessed. A comparative analysis of the photoabsorption intensities in the molecules and their constituting atoms has enabled us to predict the variation of the extent of atomic character of the molecular Rydberg orbitals with the degree of excitation. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

Spectral properties of neutral selenium and tellurium. A relativistic treatment

Oscillator strengths for fine-structure transitions in the complex atomic systems, neutral selenium, and tellurium, are reported. The calculations were carried out using the relativistic quantum defect orbital method. The resulting oscillator strengths are analyzed in terms of other theoretical and experimental data. In addition, to estimate the correctness of our oscillator strengths for these species, we have also analyzed the regularities complied by the calculated f-values. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001

Rydberg electron transitions of the atmospherically important molecule N2O

AbstractTransition intensity data on Rydberg electronic transitions of N2O, which are relevant to atmospheric and astrophysical studies, are reported. The calculations have been performed with the molecular‐adapted quantum defect orbital method, which has proven to be an adequate theoretical tool in the context of Rydberg spectra. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 70–77, 2001