The results obtained in a multiphotonic excitation of xenon near the 6s'|1/2|1 state by a tunable pulsed dye laser are presented. At low pressure the lP1 resonnant state of xenon is created by 3-photon resonnant absorption. When the pressure increases, the excitation spectra widen and shift towards shorter wavelengths. We explain this phenomenon by an excitation of the Xe2 molecules in the ground state O+g towards molecular excited state 1u(1P 1 correlated to 1P1 state. A spectral analysis showed the presence in the luminescence of the first and second continuum of xenon. We demonstrated that the third-harmonic generation of the incident laser beam intervenes in the excitation process. This radiation was detected and his pressure dependance studied. The phase matching parameter cXe and the nonlinear susceptibility were measured.