The b¹Σg⁺state of Se₂

The 4131 AA line of the krypton-ion laser populates two excited levels in 80 Se 2 , J=131, nu =5 of B0 u + and J=141 in a level with nu >or=3 of what is probably A0 u + , a component of the 3 Pi u state which is expected to be below B0 u + . The former gives rise to three fluorescence series, B0 u + -X0 g + , X1 g and b 1 Sigma g + : the latter gives a weak series terminating on b 1 Sigma g + . Lines of these four series have been recorded at high resolution by Fourier transform spectroscopy, and vibrational and rotational constants for the new state have been determined from observations in the range 1<or= nu <or=22. T e , with respect to the minimum in X0 g + , is equal to 7958.0 cm -1 .