A number of transitions in two-color resonant four-wave mixing spectra of the OH- and NH-containing flames are observed for pairs of rovibronic states without a common level. A theory is developed to show how rotationally inelastic collisions perturb the ground- and upper-state gratings and trigger new signals in equilibrium gases. The collisional alignment rate of a particular state-to-state transition in the ground vibronic state of NH is spectroscopically derived. ©2000 The American Physical Society.