Details

Autor(en) / Beteiligte

• CHRISTENSEN, RANDY B

Titel

CALCULATIONS FOR CHARGE-TRANSFER IN COLLISIONS OF TRIPLY-IONIZED NITROGEN AND DOUBLY-IONIZED SULPHUR WITH HYDROGEN ATOMS

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

1980

Link zum Volltext

• ProQuest

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• One of the most sensitive probes of the physical conditions existing in a wide variety of astrophysical plasmas is the observed distribution of several of the more abundant elements among their different ionization stages. The proper interpretation of the observations of these distributions requires detailed knowledge of the physical mechanisms that may influence them. In recent years (Weisheit, J. C. 1973, Ap. J., 185, 877 and Steigman, G. 1975, Ap. J., 199, 642) it has been suggested that non-resonant charge-transfer between multiply-charged ions and neutral hydrogen atoms may be an important neutralization mechanism for these ions. However, reliable experimental values for these reactions are not generally available. In the absence of experimental values we must rely on theoretical estimates of the relevant reaction rates. Unfortunately, there is at present no simple, universally applicable method for determining the rate of charge-transfer between any given ion and neutral hydrogen atoms. Each different ion must be treated individually. In this thesis, I first present the general theoretical approaches, based on the work of others, that are currently used in the calculation of charge-transfer collisions. Following this I present detailed descriptions of the calculations for charge-transfer of two astrophysically significant ions, N('+3) and S('+2), with hydrogen atoms. These calculations indicate that charge-transfer with H is the dominant neutralization mechanism for N('+3) over a wide range of astrophysically interesting conditions. For S('+2), on the other hand, neutralization through charge-transfer with H seems to be quite small relative to other neutralization mechanisms (e.g. radiative electron recombination). The results of this investigation serve to emphasize two important points regarding the role played by charge-transfer reactions between multiply-charged ions and hydrogen atoms in astrophysical plasmas. The first is that for certain ions charge-transfer is by far the dominant neutralization mechanism; so that any consideration of the ionization structure of a wide variety of astrophysical plasmas must consider the possible effect of charge-transfer reactions. The second is that detailed calculations are required to determine whether charge-transfer is an important neutralization mechanism for any particular ion.