Knowledge Bank

The technique of microwave-infrared double resonance has been applied to optothermally detected molecular beam spectroscopy of terminal acetylene molecules. Simplified vibrational spectra for the C-H acetylenie stretch in dth fundamental of 1-butyne and first overtone of trifluoropropyne have been obtained. In dth case of butyne, applying a modulation at the known ground state microwave frequencies allowed the assignment of die spectrum of this perturbed asymmetric top. Using upper state microwave transitions, the absorptions belonging to A or E torsional levels are distinguishable. The separation of the spectrum into torsional species is necessary in order to extract the time scale for intramolecular vibrational relaxation. For trifluoropropyne, the spectrum of the first overtone is dense with overlapping lines and only R(0) and P(1) were previously $assignable1$. Using this technique, the individual K components for other clamps have bee separated.