Equations of motion method: Excitation energies and intensities in formaldehyde

We have used the equations of motion method to study the excitation energies and intensities of electronic transitions in formaldehyde. The calculated excitation energies and oscillator strengths agree well with experiment and suggest explanations for some unusual features recently observed in the optical absorption and electron scattering spectrum of formaldehyde in the vacuum ultraviolet

A method for accurate electron-atom resonances: The complex-scaled multiconfigurational spin-tensor electron propagator method for the ^2P\, \mbox{Be}^{-} shape resonance problem

We propose and develop the complex scaled multiconfigurational spin-tensor electron propagator (CMCSTEP) technique for theoretical determination of resonance parameters with electron-atom/molecule systems including open-shell and highly correlated atoms and molecules. The multiconfigurational spin-tensor electron propagator method (MCSTEP) developed and implemented by Yeager his coworkers in real space gives very accurate and reliable ionization potentials and attachment energies. The CMCSTEP method uses a complex scaled multiconfigurational self-consistent field (CMCSCF) state as an initial state along with a dilated Hamiltonian where all of the electronic coordinates are scaled by a complex factor. CMCSCF was developed and applied successfully to resonance problems earlier. We apply the CMCSTEP method to get ^2 P\,\mbox{Be}^{-} shape resonance parameters using $14s11p5d$, $14s14p2d$, and $14s14p5d$ basis sets with a $2s2p3d$\,CAS. The obtained value of the resonance parameters are compared to previous results. This is the first time CMCSTEP has been developed and used for a resonance problem. It will be among the most accurate and reliable techniques. Vertical ionization potentials and attachment energies in real space are typically within $\pm 0.2\,eV$ or better of excellent experiments and full configuration interaction calculations with a good basis set. We expect the same sort of agreement in complex space.Comment: 13 pages, 3 figue

Transition moments between excited electronic states of N_2

We report the transition moments between the excited states of molecular nitrogen including their dependence on internuclear distance. These moments are calculated using the equations of motion method and can be obtained with only a slight increase in the effort needed to obtain the ground to excited state transition moments. The transition moments along with reliable vibrational wavefunctions should be useful in the analysis of observed band intensities of N_2

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Floquet calculations for H

We present results of calculations of rates for ionization of the lowest electronic state of the H2+ ion by a continuous-wave laser field. We solve the coupled-channel Floquet equations in both length and velocity gauges using a pseudospectral method. We employ a complex absorbing potential to obtain Siegert-type solutions resulting in resonance positions and widths. We calculate generalized cross sections for one-, two-, and three-photon ionizations for various internuclear separations of the ion with intensity of I = 1.76 × 1012 W/cm2. This is the first time the Floquet technique combined with the complex absorbing potential has been employed for photoionization cross sections of the ion. We report on ionization rates of the ion for different internuclear distances with intensity of I = 5 × 1013 W/cm2. We also present two-photon ionization cross section for different internuclear distances with intensities of I = 1.76 × 1013 and 1.76 × 1014 W/cm2. We compare our findings from calculations carried out in both gauges with those of previous calculations

Oscillator strengths for the X^1Σ^+ —A^1Π system in CH^+ from the equations of motion method

The equations of motion method is used to study the X^1Σ^+ —A^1Π system in CH^+. In a computationally simple scheme, these calculations, which were done in modest sized basis sets, provide transition moments and oscillator strengths that agree well with the best CI calculations to date

Critical analysis of equations-of-motion—Green's function method: Ionization potentials of N_2

The X ^2Σ^+_g, B ^2Σ^+_u and A ^2Π_u ionization potentials of N_2 are evaluated with the equations-of-motion (EOM)—Green's function method using four different basis sets and various forms of symmetrization. The importance of the inclusion of polarization functions is demonstrated as well as the necessity for having a basis which strikes a balance between those optimal for the neutral and ion states. With our best basis the calculated ionization potentials are within 0.35 eV of experimental values, and the results are of comparable accuracy to those obtained by Ermler with the same basis in a configuration interaction calculation with all singles and doubles with respect to the principal configuration for both the neutral and ion states

The Equations of Motion Method: An Approach to the Dynamical Properties of Atoms and Molecules

This chapter is concerned with the equations of motion method as a many-body approach to the dynamical properties of atoms and molecules. In a wide range of spectroscopic experiments one is primarily concerned with just dynamical properties. These dynamical properties include excitation energies and oscillator strengths in optical spectroscopy, the dynamic or frequency-dependent polarizability in light scattering studies, photoionization cross sections, and elastic and inelastic electron scattering cross sections. These experiments probe the response of an atom or molecule to some external perturbation. If one is concerned with these properties one should develop a formalism which aims directly at these properties. Of course this idea is not novel. For example, one might try to calculate the appropriate Green’s functions whose poles, and residues at these poles, are directly the excitation energies and transitions densities, respectively. One could also attempt to solve the time-dependent Schrödinger equation directly, e.g., in the time-dependent Hartree—Fock approximation. The approach to these dynamical properties of atoms and molecules which we will discuss is based on the equations of motion formalism as suggested by Rowe.(1) This is a very practical formalism based on the equations of motion for excitation operators defined as operators that convert one stationary state of a system into another state