High Field ESR Measurements of S=1/2 Quasi One-Dimensional Antiferromagnet Cu3Mo2O9

S=1/2 one-dimensional chain and dimer system Cu3Mo2O9, in which the super-exchange network forms one-dimensional corner-sharing tetrahedoron of Cu2+ ion, has been investigated by high field ESR measurements using the powder sample and the pulsed magnetic field up to 40 T at 2.0 K. The high field ESR measurements with wide frequency range suggest the existence of the magnetic phase transition at 8 T. Three ESR modes appear above 18 T, which corresponds to the magnetization jump. The ground state of Cu3Mo2O9 will be discuss.