  The formation and various disintegration modes of $2s$ states for muonic
hydrogen and deuterium atoms at kinetic energies both above and below the
$2s-2p$ threshold are studied. The cross sections of the collision-induced
radiative quenching, elastic scattering, and Coulomb deexcitation of $(\mu^-
p)_{2s}$ and $(\mu^- d)_{2s}$ atoms in collisions with ordinary hydrogen and
deuterium atoms at collision energies below the $2s-2p$ threshold are
calculated in the framework of the close-coupling approach. The basis set
includes all open and closed channels corresponding to exotic-atom states with
principal quantum number $n$ from 1 up to 30. Results of these numerical
quantum-mechanical calculations of cross sections are used as input data for
detailed cascade calculations. The kinetics of atomic cascade for $\mu^- p$ and
$\mu^-d$ atoms is studied in the wide range of the relative target densities,
$\varphi = 10^{-8} -1$ applying the improved version of the cascade model. It
is shown that the collision-induced radiative quenching gives a significant
contribution to the total disintegration of the $2s$ state of muonic atoms at
energies below the $2s-2p$ threshold. The initial population of the $2s$ state
for both muonic hydrogen and deuterium atoms, absolute intensities and
probabilities of the different disintegration modes as well as their lifetimes
are calculated for the fractions with kinetic energies above and below the
$2s-2p$ threshold. The obtained results are compared with the known
experimental data.
