A. M. Velasco

RYDBERG ELECTRON TRANSITIONS IN THE METHYL RADICAL

Abstract Transition probabilities corresponding to one-photon transitions to Rydberg states of the methyl radical have been calculated with a molecular-adapted version of the quantum defect orbital (QDO) method. The results appear to be in accord with those of an analysis of the experimental spectrum by Herzberg.

Oscillator strengths and ionisation cross sections for the absorption of CF2Cl2 in the UV and VUV spectral regions. A MQDO study

Abstract Absorption oscillator strengths and photoionisation cross sections of CF 2 Cl 2 have been calculated with the molecular-adapted quantum defect orbital (MQDO) approach. The differential oscillator strengths for the different Rydberg series that constitute the ionisation channels of CF 2 Cl 2 from its ground state are reported. The MQDO differential oscillator strengths exhibit the expected continuity across the ionisation threshold. In addition, good agreement with experiment is found for the cross sections that correspond to the photoionisation from the (4 b 1 +4 b 2 ) valence MO’s.

Intensity calculations of the VUV and UV photoabsorption and photoionisation of CF3Cl

Abstract Absorption oscillator strengths and photoionisation cross-sections for CF 3 Cl 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 3 Cl, 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.

Lower Rydberg series of methane: A combined coupled cluster linear response and molecular quantum defect orbital calculation

Vertical excitation energies as well as related absolute photoabsorption oscillator strength data are very scarce in the literature for methane. In this study, we have characterized the three existing series of low-lying Rydberg states of CH4 by computing coupled cluster linear response (CCLR) vertical excitation energies together with oscillator strengths in the molecular-adapted quantum defect orbital formalism from a distorted Cs geometry selected on the basis of outer valence green function calculations. The present work provides a wide range of data of excitation energies and absolute oscillator strengths which correspond to the Rydberg series converging to the three lower ionization potential values of the distorted methane molecule, in energy regions for which experimentally measured data appear to be unavailable.

Full configuration interaction calculation of the low lying valence and Rydberg states of BeH.

The all‐electron full configuration interaction (FCI) vertical excitation energies for some low lying valence and Rydberg excited states of BeH are presented in this article. A basis set of valence atomic natural orbitals has been augmented with a series of Rydberg orbitals that have been generated as centered onto the Be atom. The resulting basis set can be described as 4s2p1d/2s1p (Be/H) + 4s4p3d. It allows to calculate Rydberg states up to n= {3,4,5} of the s, p, and d series of Rydberg states. The FCI vertical ionization potential for the same basis set and geometry amounts to 8.298 eV. Other properties such as FCI electric dipole and quadrupole moments and FCI transition dipole and quadrupole moments have also been calculated. The results provide a set of benchmark values for energies, wave functions, properties, and transition properties for the five electron BeH molecule. Most of the states have large multiconfigurational character in spite of their essentially single excited nature and a number of them present an important Rydberg‐valence mixing that is achieved through the mixed nature of the particle MO of the single excitations.

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.

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.

Rotational line-integrated photoabsorption cross sections corresponding to the δ(0,0) band of NO:A molecular quantum-defect orbital procedure

The rotational line-integrated photoabsorption cross sections corresponding to the delta(0,0) band of the nitric oxide (NO) molecule at 295 K, calculated with the molecular quantum-defect orbital methodology, are in rather good accord with the experimental measurements available in the literature. The achieved results are of straightforward use in atmospheric chemistry, such as in the assessment of the NO photodissociation rate constant, which is of great relevance for atmospheric modeling.

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.

Stark maps and Rydberg transitions in the presence of an electric field for Li, Na, and K. A quantum defect orbital approach

The Stark structure of the Rydberg states of the lighter alkali atoms, Li, Na, and K, and the Stark oscillator strength distribution for Li have been calculated by diagonalization of the quantum defect orbital (QDO) Hamiltonian matrix. The presently obtained Stark maps are in excellent agreement with those resulting from theory and experiment, as reported in the literature by other authors. Good accord is also found for the presently calculated oscillator strength distribution, within a Stark manifold, with that of other theoretical approach and experimental measurements. The adequacy of the QDO procedure for accurately dealing with properties related to the Stark effect in atoms is suggested.