Beyond the electric-dipole approximation : A formulation and implementation of molecular response theory for the description of absorption of electromagnetic field radiation

• We present a formulation of molecular response theory for the description of a quantum mechanical molecular system in the presence of a weak, monochromatic, linearly polarized electromagnetic field without introducing truncated multipolar expansions. The presentation focuses on a description of linear absorption by adopting the energy-loss approach in combination with the complex polarization propagator formulation of response theory. Going beyond the electric-dipole approximation is essential whenever studying electric-dipole-forbidden transitions, and in general, non-dipolar effects become increasingly important when addressing spectroscopies involving higher-energy photons. These two aspects are examined by our study of the near K-edge X-ray absorption fine structure of the alkaline earth metals (Mg, Ca, Sr, Ba, and Ra) as well as the trans-polyenes. In following the series of alkaline earth metals, the sizes of non-dipolar effects are probed with respect to increasing photon energies and a detailed assessment of results is made in terms of studying the pertinent transition electron densities and in particular their spatial extension in comparison with the photon wavelength. Along the series of trans-polyenes, the sizes of non-dipolar effects are probed for X-ray spectroscopies on organic molecules with respect to the spatial extension of the chromophore. 

Subject headings

NATURVETENSKAP  -- Kemi -- Teoretisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Theoretical Chemistry (hsv//eng)

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Keyword

Alkaline earth metals

Barium

Chromophores

Electromagnetic fields

Energy dissipation

Organic compounds

Photons

Polarization

Quantum theory

X ray absorption

X ray spectroscopy

Assessment of results

Complex polarization propagator

Electric-dipole approximation

Electromagnetic field radiation

Forbidden transitions

Higher energy photons

Multipolar expansion

X ray absorption fine structures

Electromagnetic field theory

alkaline earth metal

magnesium

polyene

chemical structure

chemistry

conformation

electromagnetic field

photon

radiation absorption

theoretical model

Absorption

Radiation

Metals

Alkaline Earth

Models

Molecular

Models

Theoretical

Molecular Conformation

Polyenes

Publication and Content Type

ref (subject category)

art (subject category)