Femtosecond degenerate four‐wave mixing of pyridine and its biologically relevant derivatives

Time‐resolved degenerate four‐wave mixing experiments in the femtosecond time domain were employed to record the rotational ground‐state dynamics of the N‐heteroaromatic molecules pyridine, pyrimidine and pyrazine in the gas phase. Pyrimidine is an important molecular building block of several nucleic acid bases. The method records the time‐dependent change in third‐order polarization of a sample after coherent excitation. All three molecules are asymmetric tops in the oblate limit. From the analysis of the transients we obtained highly accurate averages of the two larger ground‐state rotational constants A and B.