Concepedia

Abstract

Using recent R-matrix calculations of electron excitation rates for the |$3s^23p^2P_{1/2}-3s^23p^2P_{3/2}$| fine structure transition in Si II, the electron density sensitive population ratio n(2P3/2)/n(2P1/2) has been derived for the ranges of temperature (100–20 000 K) and hydrogen density (0–1000 cm−3) applicable to H I and H II regions. The results differ appreciably from those of Smeding & Pottasch, and lead to electron density estimates approximately 30 to 40 per cent larger.