@[email protected] occurring by @[email protected] from a 'bound' to an 'unbound' vibronic state. In an @[email protected] of a molecular entity, the appearance of a diffuse band region within a series of sharp bands is called predissociation, since @[email protected] with frequencies within the diffuse region leads to effective @[email protected] The energy of the band is smaller than that of the @[email protected] continuum of the bound state.