Polarization Transfer Rates by Isotropic Collisions between Astrophysical SiO Molecule and Electrons

Moncef Derouich,Badruddin Zaheer Ahmad,Aied Alruhaili,Saleh Qutub

doi:10.3390/universe8030140

Abstract

We are interested in quantum calculations of polarization transfer (PT) rates due to collisions of the SiO molecule with the electrons. We determine the inelastic PT rates associated to the transitions: X 1Σ+→3Π; X 1Σ+→3Σ+; X 1Σ+→3Δ; X 1Σ+→3Σ−. In addition, we calculate the elastic PT rates due to rotational transitions inside the electronic state X 1Σ+ which are related to observed astronomical SiO MASERs. Our PT rates are obtained through linear combination of excitation rates previously calculated for SiO-electron collisions. The calculations are performed on a collision energy grid large enough to ensure converged state-to-state rates for temperatures ranging from 1000 to 10,000 K for inelastic rates and from 5 to 5000 K for elastic rates. The dependence of the inelastic rates on temperatures is obtained analytically and given in useful form.

Highlights

Ahmed, B.; Alruhaili, A.; Qutub, S.Interpretation of the intensity profiles of molecular lines observed in interstellar and circumstellar environments provides a wealth of knowledge about chemical abundances and physical conditions in the astrophysical media
Microwave Amplification by Stimulated Emission of Radiation (MASER) of the SiO molecule is an interesting parameter to be exploited since its polarization has been observed especially in circumstellar environments
Asensio Ramos et al (2005) [2] adopted a theoretical model based on the radiative anisotropic scattering and on the Hanle effect occurring for critical magnetic fields of ∼10−2 G to fit the observations

Summary

Introduction

Asensio Ramos et al (2005) [2] adopted a theoretical model based on the radiative anisotropic scattering and on the Hanle effect occurring for critical magnetic fields of ∼10−2 G to fit the observations. They have not taken into consideration the effects of collisions with electrons nor with hydrogen/helium atoms on the SiO MASER polarization. Derouich (2006) [7] provided quantum depolarization rates of the SiO MASER lines by collisions with hydrogen atoms but effects of collisions with electrons on the polarization of the SiO levels are yet to be investigated.

Definitions and Numerical Calculations

Rotational Rates

Astrophysical Implications

Conclusions and Perspectives