The infrared spectrum of the Ar–C2D2 complex.

Infrared spectra of Ar–C 2 D 2 are observed in the region of the ν 3 fundamental band (asymmetric C–D stretch, ≈2440 cm −1 ) using a tunable optical parametric oscillator to probe a pulsed supersonic slit jet expansion from a cooled nozzle. Transitions are assigned involving K = 0–2 in the ground vibrational state, and K = 0–4 in the excited state. The intermolecular bending combination band is also observed, giving a bending frequency of 4.798 cm −1 . Despite this low bending frequency, the Ar–C 2 D 2 spectrum qualitatively resembles that of a normal semi-rigid molecule, in contrast to He– and Ne–C 2 D 2 which are much closer to the limit of free internal rotation. [ABSTRACT FROM AUTHOR]