Quantum Defect Orbital Method Research Articles

Absorption Line Oscillator Strengths for the C 2Π(0)-A 2Σ+(0) Band of Nitric Oxide

We have determined absorption oscillator strengths for rotational transitions of the C 2Π(0)-A 2Σ+(0) band of NO, which has been detected in the upper atmosphere of Venus. The molecular quantum defect orbital method has been used in the calculation of the electronic transition moment and the Rydberg–valence interaction between the C 2Π(v = 0) and the B 2Π (v = 7) states has been considered. Considerable deviations from normal intensity distribution of the rotational lines have been found at J ≤ 5.5. As far as we know, the present line f-values are reported here for the first time. These data may be useful in the interpretation of the observations obtained by the Visible and Infrared Thermal Imaging Spectrometer instrument on the Venus Express spacecraft.

Transition Energies and Line Oscillator Strengths of the C 2Π(0)-X 2Π(0–6) Absorption Bands of Nitric Oxide. A Theoretical Study

Theoretical absorption oscillator strengths and wavelengths for rotational transitions of the C 2Π(v′ = 0)-X 2Π(v″) bands with v″ = 0–6 of nitric oxide are reported. The Molecular Quantum Defect Orbital method has been used in the calculations and the known interaction between the C 2Π(v = 0) Rydberg and the B 2Π (v = 7) valence states has been dealt with through an appropriate rovibronic energy matrix. We hope that the reported data may be useful in the analysis of the observed ultraviolet nightglow emission from nitric oxide in the upper atmospheres of Earth, Venus, and Mars.

Theoretical Study of the Rotational Structure of the c4′1Σu + (6)–X1Σg +(0–9) Absorption Bands of N2

Abstract We have theoretically determined the absorption oscillator strengths and wavenumbers for rotationally resolved transitions of the c4′1Σu + (6)-X1Σg +(0–9) bands of N2, which are relevant to analyze the spectra of planetary atmospheres. The Molecular Quantum Defect Orbital method has been used in our calculations. The interaction between the c4′1Σu + (6) Rydberg state and the b′1Σu + valence states has been considered using an adequate rovibronic energy matrix. In addition, we have calculated the lifetimes of the rotational levels of the c4′1Σu + (6) state. We hope that the reported data, most of them for the first time, can be useful in the interpretation of planetary atmospheres where N2 is present.

MgH Rydberg series: Transition energies from electron propagator theory and oscillator strengths from the molecular quantum defect orbital method

Vertical excitation energies belonging to several Rydberg series of MgH have been inferred from 3+ electron-propagator calculations of the electron affinities of MgH+ and are in close agreement with experiment. Many electronically excited states with n > 3 are reported for the first time and new insight is given on the assignment of several Rydberg series. Valence and Rydberg excited states of MgH are distinguished respectively by high and low pole strengths corresponding to Dyson orbitals of electron attachment to the cation. By applying the Molecular Quantum Defect Orbital method, oscillator strengths for electronic transitions involving Rydberg states also have been determined.

ABSORPTION OSCILLATOR STRENGTHS FOR THE (3, 4, 6)– (10, 13, 20)– AND (1)– PROGRESSIONS IN N2

ABSTRACT Absorption oscillator strengths, calculated with the molecular quantum defect orbital method, for the c 4 ′ 1 &Sgr; u + ?> (3)– X 1 &Sgr; g + ( v ″ ?> = 0–12), c 4 ′ 1 &Sgr; u + ?> (4)– X 1 &Sgr; g + ( v ″ ?> = 0–12), c 4 ′ 1 &Sgr; u + ?> (6)– X 1 &Sgr; g + ( v ″ ?> = 0–12), b ′ 1 &Sgr; u + ?> (10)– X 1 &Sgr; g + ( v ″ ?> = 0–12), b ′ 1 &Sgr; u + ?> (13)– X 1 &Sgr; g + ( v ″ ?> = 0–12), b ′ 1 &Sgr; u + ?> (20)– X 1 &Sgr; g + ( v ″ ?> = 0–12), and c 5 ′ 1 &Sgr; u + ?> (1)– X 1 &Sgr; g + ( v ″ ?> = 0–12) bands of molecular nitrogen are reported. The Rydberg–valence interaction between states of 1 &Sgr; u + ?> symmetry has been treated through an interaction matrix that includes vibrational coupling. Due to the homogeneous interaction, the intensity distribution of the bands within each progression deviates from the Franck–Condon predictions. The present results for vibronic transitions from the X 1 &Sgr; g + ( 0 ) ?> ground state agree rather well with reported high-resolution measurements. As far as we know, f-values for bands originating from v″ > 0 vibrational levels of the electronic ground state are reported here for the first time. These data may be useful in the interpretation of the extreme ultraviolet spectra from Earth’s and Titan’s atmospheres, in which several bands of the c 4 ′ ( 3 ) , ?> c 4 ′ ( 4 ) , ?> and c 4 ′ ( 6 ) ?> progressions have been identified.

Photoionization cross sections and asymmetry parameters for ethanol. A theoretical study

Photoionization cross-sections and asymmetry parameters for the outermost orbital of ethanol have been determined with the Molecular Quantum Defect Orbital (MQDO) method. The individual ionization cross-sections corresponding to the Rydberg series that constitute the ionization channels for the production of the molecular cation in its ground state are reported. Good agreement has been found with the experiment for the photoionization cross-sections. To our knowledge, predictions of the asymmetry parameter for the ethanol are made here for the first time. It is hoped that the MQDO data will be useful in combustion chemistry and astrophysics.

Excitation energies, photoionization cross sections, and asymmetry parameters of the methyl and silyl radicals.

Vertical excitation energies of the methyl and silyl radicals were inferred from ab initio electron propagator calculations on the electron affinities of CH3(+) and SiH3(+). Photoionization cross sections and angular distribution of photoelectrons for the outermost orbitals of both CH3 and SiH3 radicals have been obtained with the Molecular Quantum Defect Orbital method. The individual ionization cross sections corresponding to the Rydberg channels to which the excitation of the ground state's outermost electron gives rise are reported. Despite the relevance of methyl radical in atmospheric chemistry and combustion processes, only data for the photon energy range of 10-11 eV seem to be available. Good agreement has been found with experiment for photoionization cross section of this radical. To our knowledge, predictions of the above mentioned photoionization parameters on silyl radical are made here for the first time, and we are not aware of any reported experimental measurements. An analysis of our results reveals the presence of a Cooper minimum in the photoionization of the silyl radical. The adequacy of the two theoretical procedures employed in the present work is discussed.

Angular distribution of photoelectrons in small molecules: A molecular quantum defect calculation

The molecular quantum defect orbital (MQDO) method, previously used in the determination of molecular photoionization cross sections, is applied here to calculate the angular distribution of photoelectrons arising from the molecular photoionization. Calculations are performed for the ionization from outer valence orbitals of HF, H(2)O, NH(3), N(2)O, and H(2)CO molecules. The results are compared with previous measurements and with theoretical curves found in the literature. Profiles of the angular distribution parameter as a function of photoelectron energy covering a range from the photoionization threshold to 120 eV are presented for the above molecules. The energy dependence of the angular distributions predicted by the MQDO calculations agrees fairly well with predictions from more sophisticated theories and with observed results.

LINE ABSORPTION OSCILLATOR STRENGTHS FOR THE c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(0-5) BANDS IN N{sub 2}

Theoretical absorption oscillator strengths and emission branching ratios for rotational lines of the c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(0-5) bands of molecular nitrogen are reported. The calculations have been performed with the molecular quantum defect orbital method, which has proved to be reliable in previous studies of rovibronic transitions in diatomic molecules. The strong interaction between c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3) and b' {sup 1}{Sigma}{sup +}{sub u}(10) states has been analyzed through an interaction matrix that includes rotational terms. Owing to the perturbation, the c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(0), c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(1), and c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3)-X{sup 1}{Sigma}{sup +}{sub g}(5) bands are not weak, in contrast to what would be expected on the basis of the Franck-Condon principle. Moreover, the intensity distribution of the rotational lines within each of the vibronic bands deviates from considerations based on Hoenl-London factors. In this work, we provide data that may be useful to interpret spectra from atmospheres of the Earth, Titan, and Triton, in which transitions from the c'{sub 4}{sup 1}{Sigma}{sup +}{sub u}(3) level have been detected.

LINE ABSORPTION OSCILLATOR STRENGTHS FOR THEc′41Σ+u(3)-X1Σ+g(0-5) BANDS IN N2

Theoretical absorption oscillator strengths and emission branching ratios for rotational lines of the c'4 1Σ+ u (3)-X 1Σ+ g (0-5) bands of molecular nitrogen are reported. The calculations have been performed with the molecular quantum defect orbital method, which has proved to be reliable in previous studies of rovibronic transitions in diatomic molecules. The strong interaction between c'4 1Σ+ u (3) and b' 1Σ+ u (10) states has been analyzed through an interaction matrix that includes rotational terms. Owing to the perturbation, the c'4 1Σ+ u (3)-X 1Σ+ g (0), c'4 1Σ+ u (3)-X 1Σ+ g (1), and c'4 1Σ+ u (3)-X 1Σ+ g (5) bands are not weak, in contrast to what would be expected on the basis of the Franck-Condon principle. Moreover, the intensity distribution of the rotational lines within each of the vibronic bands deviates from considerations based on Honl-London factors. In this work, we provide data that may be useful to interpret spectra from atmospheres of the Earth, Titan, and Triton, in which transitions from the c'4 1Σ+ u (3) level have been detected.

Electronic spectrum of F2CO: theoretical calculations of vertical excitation energies and intensities

In this work, the linear response formalism with a triples-corrected CCSD reference wave function, LR-CCSDR(3), is applied to the calculation of vertical excitation energies of singlet states of the F2CO molecule. A basis set of atomic natural orbitals augmented with a series of Rydberg functions has been used in the calculations. A large number of electronically excited states were calculated, and the valence, Rydberg, or mixed character of the states were investigated. In addition, the molecular quantum defect orbital (MQDO) method has been used to determine transition intensities involving Rydberg states. Excitation energies and transition intensities for Rydberg states with n > 3 are reported for the first time.

Oscillator strengths and photoionisation cross sections for Rydberg transitions in acetaldehyde

Oscillator strengths for electronic transitions involving Rydberg states of acetaldehyde, as well as cross sections for all the dipole allowed photoionisation channels, all ending in the ground state of the molecular cation, are reported. The molecular quantum defect orbital method, which has proved to be reliable in previous applications to molecular Rydberg states, has been used. Despite its relevance for atmospheric chemistry and astrophysics, only a few data seem to be available in the literature. The continuity of the calculated differential oscillator strength across the ionisation threshold has been adopted as a quality criterion. To our knowledge, predictions of oscillator strengths for transitions to high-lying Rydberg states, as well as of photoionisation profiles on acetaldehyde are made here for the first time and we are not aware of any reported experimental data. We, thus, hope the present results may be useful in the interpretation of the spectrum of acetaldehyde and might be of help in future experimental measurements.

Rotational line intensities of the [formula omitted] bands of N 2

Oscillator strengths and integrated cross-sections for rotational lines of the c 4 ′ 1 Σ u + ( 1 ) - X 1 Σ g + ( 0 - 2 ) bands of N 2 have been calculated with the molecular quantum defect orbital (MQDO) method. The known strong homogeneous interaction of the c 4 ′ 1 Σ u + ( 1 ) Rydberg state with the b′ 1 Σ u + ( 4 ) valence state has been presently dealt with through an interaction matrix for each value of the rotational quantum number, J. Because of perturbations, the intensity distribution of the rotational lines within each of the vibronic bands deviates from the predictions based on Hönl–London factors. Band oscillator strengths are also reported and their J-dependence has been analyzed.

Partial photoionization cross sections of NH4 and H3O Rydberg radicals

Photoionization cross sections for various Rydberg series that correspond to ionization channels of ammonium and oxonium Rydberg radicals from the outermost, occupied orbitals of their respective ground states are reported. These properties are known to be relevant in photoelectron dynamics studies. For the present calculations, the molecular-adapted quantum defect orbital method has been employed. A Cooper minimum has been found in the 3sa(1)-kpt(2) Rydberg channel of NH(4) beyond the ionization threshold, which provides the main contribution to the photoionization of this radical. However, no net minimum is found in the partial cross section of H(3)O despite the presence of minima in the 3sa(1)-kpe and 3sa(1)-kpa(1) Rydberg channels. The complete oscillator strength distributions spanning the discrete and continuous regions of both radicals exhibit the expected continuity across the ionization threshold.

Theoretical Study of Spectral Intensities of Formaldehyde in the Discrete and Continuum Regions

Theoretical absorption oscillator strengths for transitions involving Rydberg states in molecular formaldehyde as well as cross sections for photoionization Rydberg channels associated with the production of the lowest parent ion electronic state are reported. The calculations have been performed with the molecular quantum defect orbital (MQDO) method. A test on the MQDO f values has been its comparison with previous experiments and calculations and its compliance with the expected systematic trends along the Rydberg series. The use of the MQDO method as an alternative to ab initio methods, which find serious difficulties in calculating spectral intensities in formaldehyde, is proposed. We hope that the spectroscopic data, many of them reported here for the first time, may be useful for the interpretation of the vacuum ultraviolet spectrum of this molecule.

Theoretical calculation of the rotational structure of the (0, 0) and (0, 1) bands of the system of N2

Theoretical absorption oscillator strengths and line-integrated rotational cross sections for both the (0, 0) and (0, 1) bands belonging to the electronic transition of molecular nitrogen, which are relevant to the study of the atmospheres of the Earth, those of planetary satellites, as well as of the interstellar medium, are reported. The calculations were performed with the molecular quantum defect orbital method. The results for the (0, 0) band are in rather good agreement with reported measurements corresponding to vacuum ultraviolet photo-absorption spectra. We hope that the line oscillator strengths for the (0, 1) band reported here for the first time may be useful in the analysis of observations from space missions, and might aid in the design of future experimental measurements.

Spontaneous radiative decay rates in Ga-like ions

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. Atomic data, such as wavelengths and transition rates for 4p3/2 → 4p1/2 emission lines in the gallium sequence have been calculated with the Relativistic Quantum Defect Orbital (RQDO) method. The present results are tested by comparison with other theoretical values available in the literature. The regularity of the transition intensities along the isoelectronic sequence for both (E2 and M1) lines, as well as their relative magnitude, are also analyzed. M1 transitions were found to dominate by at least a factor of ten times, being in many cases bigger that this. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Spectral Properties of Hydrogen Fluoride in the Discrete and Continuum Regions (Rydberg Series in Hydrogen Fluoride)

Hydrogen fluoride has been observed in a number of astrophysical environments, being sizably abundant in some of them, which adds to the interest in the processes in which it participates. The processes that have called for our attention are those that involve the interaction of photons or electrons with HF, as they are largely responsible for the evolution of chemical abundances in such environments. On the other hand, the spectral features of HF are, in a sense, anomalous. This fact has been attributed to the interaction between some of the valence and Rydberg states of the molecule and has motivated us to undertake these calculations. The present work deals with the calculation of absorption oscillator strengths involving Rydberg states of hydrogen fluoride, as well as of differential oscillator strengths for the dipole-allowed photoionization channels of HF, all ending in the ground X 2Π state of HF+. The calculations have been performed with the molecular adapted quantum defect orbital (MQDO) method, which has proved to be reliable in previous studies. It is our belief that the achieved data, reported here for the first time, may be useful in studying the evolution of chemical abundances in important astronomical objects and might aid in future experimental measurements.

Ground and excited states of the Rydberg radical H3O: Electron propagator and quantum defect analysis

Vertical excitation energies of the Rydberg radical H(3)O are inferred from ab initio electron propagator calculations on the electron affinities of H(3)O(+). The adiabatic ionization energy of H(3)O is evaluated with coupled-cluster calculations. These predictions provide optimal parameters for the molecular-adapted quantum defect orbital method, which is used to determine oscillator strengths. Given that the experimental spectrum of H(3)O does not seem to be available, comparisons with previous calculations are discussed. A simple model Hamiltonian, suitable for the study of bound states with arbitrarily high energies is generated by these means.

MQDO oscillator strengths and emission coefficients for electronic transitions in N 2 and NO

The molecular-adapted quantum defect orbital (MQDO) method has been applied to the calculation of absorption oscillator strengths and Einstein emission coefficients for electronic transitions involving Rydberg states of N 2 and NO. These compounds have been found to play an important role in the evolution of Earth's upper atmosphere. However, the difficulties encountered in both laboratory measurements and theoretical calculations on the photoabsorption of these compounds are responsible for the scarcity of data in the literature. Predictions of unknown transition probabilities for the NO molecule are presently given.