  A search is conducted for new physics in a final state containing a photon
and missing transverse momentum in proton-proton collisions at sqrt(s) = 13
TeV. The data collected by the CMS experiment at the CERN LHC correspond to an
integrated luminosity of 12.9 inverse femtobarns. No deviations are observed
relative to the predictions of the standard model. The results are interpreted
as exclusion limits on the dark matter production cross sections and parameters
in models containing extra spatial dimensions. Improved limits are set with
respect to previous searches using the monophoton final state. In particular,
the limits on the extra dimension model parameters are the most stringent to
date in this channel.
