Effect of exchange and absorption potential in the distorted wave calculation of electron impact excitation of auto ionizing state of rubidium
Agutu, Vincent Onyango Othieno Nunda
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Study of electron impact excitation of autoionizing states of alkali atoms is very important because it can explain the additional peaks which appear in the ionization curve of the alkali atoms. Very many researches have been made on the research of electron impact excitation of autoionizing states of alkalis using close coupling method, R-matrix and Distorted Wave Method. But in the Distorted Wave applied to electron impact excitation of rubidium atom only the real potential i.e. static or static and exchange potential has been used. That is why in this study complex distortion potential which includes static, exchange and absorption potential, has been used for electron impact excitation of lowest autoionizing state of rubidium atom using a distorted wave method. Initial and final state wave function of the projectile electron is distorted by the complex potential. Differential and integral cross section and angular correlation parameter have been calculated and compared with the available theoretical and experimental results. Numerical calculations have been done using a modified dwbal fortran computer program which was originally made for hydrogen atom. From the comparison of the results, it is observed that in general the electron impact excitation cross section results are higher around excitation threshold energy. This can be attributed to the exchange process which takes place in the case of electron impact and also due to larger interaction between the projectile and the target. It is also observed that the absorption potential lowers the cross section and brings it closer to the experimental results. Alignment parameter results indicate that the integral cross section results for m=O level are larger compared to m=1 level for impact energies up to about 400eV beyond which integral cross-sections for the magnetic sublevel m=1 become greater. The lambda parameter indicates that more particles are scattered towards m=O for electron impact.