  Proton irradiation of both n-type and semi-insulating bulk samples of
\b{eta}-Ga2O3 leads to the formation of one paramagnetic defect with spin
S=1/2, monoclinic point symmetry, a g-tensor with principal values of
gb=2.0313, gc=2.0079, ga*= 2.0025 and quasi isotropic superhyperfine
interaction of 13G with two equivalent Ga neigbours. Its high introduction rate
indicates it to be a primary irradiation induced defect. At low temperature,
photoexcitation transforms this defect into a different metastable S=1/2 center
with principal g-values of gb=2.0064, gc=2.0464, ga*= 2.0024 and a reduced
hyperfine interaction of 9G. This metastable defect is stable up to T=100K,
when it switches back to the previous configuration. Density functional theory
calculations of the Spin Hamiltonian parameters of various intrinsic defects
are carried out using the Gauge Including Projector Augmented Wave method in
order to determine the microscopic structure of these defects.Our results do
not support the intuitive model of the isolated octahedral or tetrahedral
gallium vacancy, VGa2-, but favor the model of a gallium vacancy complex
VGa-Gai-VGa.
