In a frequency-modulation spectroscopy experiment, using the radiation from a single frequency diode laser, the
spectra of molecular iodine hyperfine structure near 640 nm were recorded on the transition B<sup>3</sup>Π<sup>+</sup><sub>0u</sub>- X<sup>1</sup>Σ<sup>+</sup><sub>g</sub> .
The frequency reference given by the value of the modulation frequency (12.5 MHz in given experiment) allows
determination of the frequency differences between hyperfine components with accuracy better than 0.1 MHz
using the fitting procedure in experiment with only one laser.
The interaction of a linear polarized weak probe wave with the molecular iodine driven by the strong pump wave with
the orthogonal polarization is experimentally studied. An effect of electromagnetically induced transparency (EIT) is
observed. The group velocity of the probe wave is decreased to 0,13<i>c</i>.
The interaction of circularly polarized weak probe wave with the molecular iodine driven by the strong pump wave with the opposite polarization has been theoretically studied. It is shown that the phenomenon of electromagnetically induced transparency in the iodine vapour can be observed for moderate intensity (~10-100 W/cm<sup>2</sup>) of the pump wave. The group velocity of the probe wave can decrease to 0.1c.