Using,a pulsed supersonic slit nozzle, the nonfluorescing pi*<--n transition of pyridazine was investigated. The degenerate four wave mixing (DFWM) spectra showed numerous vibrational bands over a 1200 cm(-1) region. Most of these bands were parallel transitions with a strong Q branch and weaker but observable P and R branches. Based on our previous model [H. Li and W. Kong, J. Chem. Phys. 107, 3774 (1997)] these transitions were simulated with success. The polarization dependence of the rotational branching ratios suggested that primary contributions to the DFWM signal were from large spaced gratings formed by ground state molecules. The lack of contributions from excited state gratings and small spaced gratings was attributed to the fast internal conversion process on the S-1 surface of pyridazine (0.3-3 ns), the wash-out time due to movements of the sample in a molecular beam, and the duration time of the excitation laser (7 ns). Two vibrational bands showed unexpected enhancement in the P or R branch, but for each band, one adjustment factor was sufficient to reproduce the spectra recorded under all different polarization combinations. Perturbations were observable from the rotationally resolved spectra, however in most cases, rotational progressions did not seem to be affected by the perturbation in terms of both line positions and intensities. A more detailed analysis of the supersonically cooled spectra, together with data from a room temperature gas cell and ab initio calculations, will be necessary to completely interpret the spectroscopy of pyridazine. This paper demonstrates that with the increased sensitivity achievable through a slit nozzle, DFWM is an effective technique for detailed spectroscopic studies, particularly for nonfluorescing species.