Atomic oscillator strength
= Atomic oscillator strength
{title2=$f_{ij}$}
An atomic oscillator strength is a dimensionless measure of an optical transition's absorption strength relative to a classical electron oscillator. It is related to its spontaneous radiative rate through the transition energy and the statistical weights of the two levels. The absorption convention $f_{ij}$ fixes the lower state $i$ and upper state $j$; interchanging that convention can lose a weight factor.