EINSTEIN $A$-COEFFICIENTS AND STATISTICAL WEIGHTS FOR MOLECULAR ABSORPTION TRANSITIONS IN THE $HITRAN$ DATABASE

Abstract

The weighted square of the transition moment presented in previous editions of $HITRAN$ has been replaced by the Einstein $A$-coefficient in $HITRAN$ 2004. The calculation has been performed using the $HITRAN$ line intensities $S_{HIT}$, the statistical weights $g_2$ of the upper levels and other related quantities \vspace{1em} $A_{21}=8{\pi}c{\nu}0^2Q{tot}(T_0)S_{HIT}/(e^{-c_2E_1/T_0}(1-e^{-c_2{\nu}_0/T_0})I_ag_2)$. \vspace{1em} The motivations and the corresponding theory, including the determination of the statistical weights for molecules of various symmetries, will be discussed.