  The influence of reaction order and trap-assisted recombination on
continuous-wave photoinduced absorption measurements is clarified through
analytical calculations and numerical simulations. The results reveal the
characteristic influence of different trap distributions and enable
distinguishing between shallow exponential and Gaussian distributions as well
as systems dominated by direct recombination by analyzing the temperature
dependence of the in-phase and quadrature signals. The identifying features are
the intensity dependence of the in-phase at high intensity,
$\textit{PA}_\text{I}\propto I^{\gamma_\text{HI}}$, and the frequency
dependence of the quadrature at low frequency, $\textit{PA}_\text{Q}\propto
\omega^{\gamma_\text{LF}}$. For direct recombination $\gamma_\text{HI}$ and
$\gamma_\text{LF}$ are temperature independent, for an exponential distribution
they depend on the characteristic energy $E_\text{ch}$ as
$\gamma_\text{HI}=1/(1+E_\text{ch}/kT)$ and $\gamma_\text{LF}=kT/E_\text{ch}$
while a Gaussian distribution shows $\gamma_\text{HI}$ and $\gamma_\text{LF}$
as functions of $I$ and $\omega$, respectively.
