A laser-ablation molecular-beam Fourier-transform microwave spectrometer: The rotational spectrum of organic solids

A spectrometer that combines laser ablation of a solid sample with molecular-beam Fourier-transform microwave spectroscopy (MB-FTMW) has been constructed to obtain the rotational spectrum of solid organic molecules. Laser ablation is produced by visible radiation, using the second harmonic of a Nd:YAG laser. The laser hits a solid rod placed on a specially designed pulsed nozzle, coaxially oriented with the axis of the microwave spectrometer Fabry–Pérot cavity. The vaporized molecules are seeded in the supersonic jet formed by the expansion of a carrier gas (Ar,Ne) and probed by FTMW spectroscopy. The high sensitivity of the spectrometer is exemplified with the observation of minor isotopomers in natural abundance of different organic molecules and natural amino acids. This instrument opens perspectives in the investigation of the gas phase structure of solid organic compounds.