Vibrational Excitation Cross-Section by Positron Impact: A Wave-Packet Dynamics Study

Luis A Poveda,José R Mohallem,Marcio T Do N Varella

doi:10.3390/atoms9030064

Abstract

The vibrational excitation cross-section of a diatomic molecule by positron impact is obtained using wave-packet propagation techniques. The dynamics study was carried on a two-dimensional potential energy surface, which couples a hydrogenlike harmonic oscillator to a positron via a spherically symmetric correlation polarization potential. The cross-section for the excitation of the first vibrational mode is in good agreement with previous reports. Our model suggests that a positron couples to the target vibration by responding instantly to an interaction potential, which depends on the target vibrational coordinate.

Highlights

A fundamental question in positron–matter interaction is how a positron couples to the vibrational modes of molecules, after experimental measurements [1,2,3] and theoretical models [4,5,6,7,8,9,10,11] agree appreciably for vibrational excitation cross-sections for low-energy positron–molecule scattering
Our results show the typical behavior of the cross-section with a sharp onset at threshold, followed by a peak with maximum around 0.5 a.u. height, falling down to zero as the energy increases
It becomes arguable that the coupling between the positron and the first vibrational mode of the target can be accounted for by the instantaneous response of the molecule to the positron through the R-dependent attractive correlation polarization potential

Summary

Introduction

A fundamental question in positron–matter interaction is how a positron couples to the vibrational modes of molecules, after experimental measurements [1,2,3] and theoretical models [4,5,6,7,8,9,10,11] agree appreciably for vibrational excitation cross-sections for low-energy positron–molecule scattering. The computed 0 → 1 vibrational excitation cross-section displays good agreement with previously reported experimental and theoretical results, suggesting that the oscillator embedded in the positron continuum couples to it through a correlation polarization force, which depends on the target oscillatory coordinate. Atomic units are assumed throughout the text, unless otherwise stated

The Model Potential

Wave-Packet Dynamics

Results and Discussion

Conclusions