We measured the in flight annihilation frequencies and cross sections of reactions (n) over bar p --> pi(+) pi(0), pi(+) eta and K+KS in the antineutron momentum range between 50 and 400 MeV/c. The annihilation frequencies of these channels from the different allowed initial states were calculated and some information about the (n) over bar p annihilation dynamics were obtained. The first determination of the D-wave contribution in this momentum range was also obtained. (C) 1997 Published by Elsevier Science B.V