Calculations of gamma-ray spectral profiles of linear alkanes in the positron annihilation process

Abstract

The positron-electron annihilation gamma-ray spectra of linear alkanes C n H 2n+2 (n=1-12) have been studied systematically. A profile quality (PQ) parameter, χ, is introduced to assess the agreement between the obtained theoretical profiles and the experimental measurements in the entire region of energy shift of the spectra. Together with the Doppler shift (∆ε) of the gamma-ray spectra, the two parameters, χ and ∆ε, are able to provide a more comprehensive assessment of the calculated gammaray spectra with respect to available experiment. Applying the recently developed docking model, the present study determines the positrophilic electrons for individual alkanes from which the gamma-ray spectral profiles are calculated. The results achieve an excellent agreement with experiment, not only with respect to the Doppler shift, but also with respect to the gamma-ray profiles in the photon energy region up to 5 keV. The study further calculates the gamma-ray spectra of other linear alkanes in the series without available experimental measurements, such as heptane (C 7 H 16 Keywords: Gamma-ray spectra of alkanes; positron-electron annihilation profile quality; positrophilic electrons; lowest occupied valence orbital (LOVO); local molecular attraction potential (LMAP).

Quantum chemical approach for positron annihilation spectra of atoms and molecules beyond plane-wave approximation

“…Conversely, the valence MOs have small FWHMs and large contributions. Here, we mention the lowest occupied valence orbitals (LOVO), which have attracted attention in previous PWP studies [25][26][27][28][29]31 because of the agreement with the FWHM of the experimental spectra. FWHMs.…”

“…5,6,[9][10][11][12][13][14][15][16][17] In addition, the annihilation spectra of molecules and noble gas atoms have been analyzed using the plane-wave positron (PWP) method. [18][19][20][21][22][23][24][25][26][27][28][29][30] The PWP method approximates the positronic wavefunction as a plane wave, while the electronic state is determined by a quantum chemical calculation. However, the PWP method severely overestimates a) Author to whom correspondence should be addressed: nakai@waseda.jp.…”

Positron-Electron Annihilation Process in (2,2)-Difluoropropane Molecule

“…Hence, in (2,2)-difluoropropane molecule, the two fluoride atoms will dominate the annihilation process rather than the carbon atoms in propane. [32] Fig. 3 (Color online) The local molecular attraction potential (LMAP) of (2,2)-difluoropropane.…”

“…[3] Furthermore, the studies have also shown that there are some special valence electrons in atoms and molecules, which are correlated strongly experimental gamma-ray spectra. [32] These electrons, we called positrophilic electrons, [32−34] are usually underneath the outer valence orbital, and called inner valence electrons.…”