  We study the Autler Townes (AT) effect derived from a strong electric dipole
transition stimulated by a resonant laser beam and probing it by means of a
weak electric quadrupole transition with a controlled frequency detuning in a
ladder configuration. The experiment was carried out for a $^{87}$Rb atomic gas
at room temperature in a velocity-selective scheme. The AT effect was monitored
via the splitting of the fluorescence spectra associated with the spontaneous
decay to the ground state. The theoretical description incorporates the
modification of standard few-level schemes introduced by forbidden
electric-dipole transitions selection rules. We develop an analytic ladder
three-level scheme to approximate the cyclic $5\mathrm{S}_{1/2}
\mathrm{F}=2\rightarrow 5\mathrm{P}_{3/2} F=3 \rightarrow 6\mathrm{P}_{3/2}
\mathrm{F}=1,2,3\rightarrow 5 \mathrm{S}_{1/2}\mathrm{F}=2$ path. Other levels
that could have effects on the fluorescence are included via a fourth level
with effective parameters. Doppler effects and finite bandwidths of the laser
beams are included in the theoretical model to closely reproduce the
experimental results.
