High resolution spectroscopy of the 2CH band in the 12C2H2–Ar van der Waals complex

We have used CW cavity-ring-down-spectroscopy around 1.5 μm to probe a free supersonic expansion of mixed acetylene and Argon. The high resolution spectrum of the 2CH band in the 12C2H2–Ar van der Waals complex was recorded, at a rotational temperature of about 15 K. Upper state spectroscopic constants are provided from the fit of the 44 assigned vibration–rotation lines in the Ka = 0 ← 1 and 1 ← 0 sub-bands to a conventional Watsonian.