Observation of dipole–quadrupole radiative collisional fluorescence

The first known observation of spontaneous dipole-quadrupole radiative emission during the collision of an excited Ba atom with an excited Ti atom is reported. The emission occurs at the sum energy of the excited atoms and is the dipole-quadrupole analog of the dipole-dipole emission process recently reported. A collision cross section for spontaneous radiative de-excitation of 1.5 X 10(-22) cm2 is measured.