New electronic transitions of KRb are identified near 530 nm by resonance enhanced two photon ionization study in a supersonic molecular beam. The rotational structure shows O, P, Q, R, and S branches. From the high resolution rotational analysis and comparison with the spectra of other alkali diatomic molecules we assign the observed bands to the 1 (1)Delta -X (1)Sigma (+) transitions of KRb, which are allowed by electric quadrupole radiation. We obtain molecular constants for the upper electronic state of (KRb)-K-39-Rb-85 as omega (e)=64.624 1(35)cm(-1), T-e=18 991.011 0(14)cm(-1), B-e(')=0.035 703 9(10)cm(-1), and R-e=4.204 55(6) A. Another new electronic transition observed in the same wavelength region is assigned to the 3 (3)Sigma (+)-X (1)Sigma (+) transition from the comparison with ab initio calculations. (C) 2001 American Institute of Physics.