Bound states of positron with simple carbonyl and aldehyde species with configuration interaction multi-component molecular orbital and local vibrational approaches

Abstract

Characteristic features of the positron-binding structure of some carbonyl and aldehyde species such as formaldehyde, acetaldehyde, acetone and propionaldehyde are discussed with the configuration interaction scheme of multi-component molecular orbital (MC MO) calculations. This method can take the electron-positron correlation contribution into account through single electronic-single positronic excitation configurations. Our vertical positron affinity (PA) values of acetaldehyde and acetone with electronic 6-31++G(2df,2pd) and positronic [15s15p3d2f1g] basis sets are as 52 and 92 meV, which can be compared to the recent experimental values of 90 and 173 meV by Danielson et al (2010 Phys. Rev. Lett. 104 233201). For formaldehyde we have also found that the PA values are enhanced by including the local C O vibrational contribution from the vertical PA value of 15 meV to 17, 21 and 25 meV after averaging over the zeroth, first and second vibrational states, respectively, due to the anharmonicity of the potential.

Calculation of positron binding energies using the generalized any particle propagator theory

“…Efforts in this direction have been conducted by Tachikawa and coworkers. They have calculated PBEs for several polyatomic molecules 22,[27][28][29][30][31][32][33] employing the multi-component molecular orbital Hartree-Fock (MCMO/HF) approach. Although this method provides fair qualitative PBEs at a reasonable numerical effort, results are still underestimated with respect to experimental data and high-level calculations.…”

Effect of dipole polarizability on positron binding by strongly polar molecules

“…This justifies the hard-sphere model for the short-range positron repulsion. Quantum chemistry calculations of the positron density in polar molecules support the picture of a diffuse positronic cloud localized off the negatively charged end of the molecular dipole [14,17,19,20]. Note that a recent paper [22] combined a hard-sphere repulsive core with the polarization potential to model positron binding to atoms and nonpolar molecules.…”

“…Placing HCN in the ketone family led to a predicted binding energy of 70 meV, which is a factor of two greater than the DMC result of [17]. This large value is likely an overestimate, in spite of the fact that quantum chemistry calculations tend to give lower bounds for the positron binding energies [19,20]. Experimental data for ketones shows significant deviations from linearity (see figure 5), which makes the ketone-based prediction for HCN less relaible.…”

“…It accounts for the next order corrections in both (20) and (21), and extends the applicability of (23) way beyond the range of near-critical µ. Regarding the constants A, B and C as fitting parameters, an excellent fit of the numerical data over the whole range covered by figure 3 is obtained using A = 65 998.7 meV, B = 12.2705 D 1/2 and C = 0.400 612 D −1/2 , and the dipole moment µ in debye (D).…”

Formation of positron-atom bound states in collisions between Rydberg Ps and neutral atoms

“…The zero-range potential model [23,24] captured the qualitative features for the alkanes, and there were configuration-interaction (CI) calculations for carbon-containing triatomic molecules [25,26]. For strongly polar molecules many quantum-chemistry calculations have been performed, but only a few of them allow direct comparison with experiment; recent CI calculations for nitriles, aldehydes, and acetone [27][28][29] gave binding energies within 25-50% of experimental values. A simple theoretical model was recently proposed to explain the dependence of the binding energy on the molecular dipole moment and dipole polarizability [30].…”