A (4+2) RESONANCE ENHANCED MULTIPHOTON IONIZATION STUDY OF THE B1S+ STATE= OF CO F.B.Yousif, I.Alvarez, C.Cisneros, J.de Urquijo, J.P.Flores Centro de Ciencias Fisicas, UNAM, P.O. Box 48-3, Cd. Post. 62251 Cuernavaca, Mor., Mexico The four photon excitation of the B1S+ state has been investigated with resonance enhanced multiphoton ionization spectroscopy with linearly polarized light. The results show that the excitation to v=A2 =3D 0 is = dominant in accordance with the theoretical predictions and the selection rules.