[en] We derive fully covariant expressions for all two-point scattering amplitudes involving a closed string tachyon and massless strings from the Dirichlet brane in type 0 theories. The amplitude for two massless D-brane fluctuations to produce a closed string tachyon is also evaluated. We then examine in detail these string scattering amplitudes in order to extract world-volume couplings of the tachyon with itself and with massless fields on a D-brane. We find that the tachyon appears as an overall coupling function in the Born-Infeld action and conjecture the form of the function