We model the effects of a quasibound photonic state that can exist within a substrate/metal film/Bragg reflector/air structure. The photonic state is confined as a result of total internal reflection at the air interface coupled with the effect of the photonic band gap of the Bragg reflector. The presence of the thin metallic film ensures that distinctive features are observable in the associated reflectivity spectrum. With an appropriately chosen metal layer thickness, light is able to penetrate into the structure but is then effectively trapped, leading to a greatly increased field intensity at the air interface and an associated sharp feature in the reflectivity. The sensitivity of the reflectivity feature to structural details and angle of incidence and the property of substantial field enhancement suggest that the structure could be of use in sensor/detector technology and nonlinear optics applications.