This work investigates interacting states in polyatomic molecules, concentrating on two examples, the analysis of interacting states in the linear C3 radical and the study of perturbations resulting from interacting states in Formaldehyde. Work on the C₃ radical started with ab initio potential energy surface calculations to outline the lowest 8 singlet electronic states, followed by vibrational energy level calculations corresponding to these electronic states. On the experimental front, the vibronic states of the radical were probed by laser spectroscopy, particularly by double resonance techniques.