  Radiative deexcitation (RD) of the metastable 2S state of muonic protium and
deuterium atoms has been observed. In muonic protium, we improve the precision
on lifetime and population (formation probability) values for the short-lived
{\mu}p(2S) component, and give an upper limit for RD of long-lived {\mu}p(2S)
atoms. In muonic deuterium at 1 hPa, 3.1 +-0.3 % of all stopped muons form
{\mu}d(2S) atoms. The short-lived 2S component has a population of 1.35 +0.57
-0.33 % and a lifetime of {\tau}_short({\mu}d) = 138 +32 -34 ns. We see
evidence for RD of long-lived {\mu}d(2S) with a lifetime of {\tau}_long({\mu}d)
= 1.15 +0.75 -0.53 {\mu}s. This is interpreted as formation and decay of
excited muonic molecules.
