Knowledge Bank

The infrared spectrum of argon-acetylene has been recorded in the three micron wavelength region by observing direct absorption of color center laser radiation by a pulsed molecular beam. Thirty transitions in the , and bands of a perpendicular transition have been assigned. The origin of this Ar-HCCH vibrational transition is about $0.3cm-1$ lower in energy than the $\nu 3$ monomer origin. The rotational structure yields values for A and B-C which are consistent with an earlier radio frequency spectrum of Ar-HCCH. However, (B+C)/2 from the infrared spectrum is much smaller than the earlier prediction. Argon acetylene exhibits an extremely large inertial defect, which explains the poor prediction based on the radio frequency spectrum.