Difference-frequency laser spectroscopy of gas phase C2D in the 2800 cm - 1 region

The gas phase C₂D absorption spectrum has been studied in the 2800 cm^-1 region using a high resolution difference-frequency laser spectrometer. The C₂D molecules were produced in a hollow cathode discharge in a mixture of C₂H₂ or C₂D₂ (∼20 mTorr) and D₂ (∼400 mTorr). Two bands were identified and rotationally analyzed. One band at 2796 cm^-1 was found to be a ²Π-²Σ⁺ transition with the lower state being the ground state. The upper level of this band is assigned to the (110) state in the ground electronic state, X∼ ²Σ⁺. The other band at 2851 cm^-1 is a ²Σ⁺-²Σ⁺ transition from the (001) state in X∼ ²Σ⁺ to a vibronic ²Σ⁺ state which was found to be perturbed. Accurate molecular constants for the upper levels involved were determined from least-squares fit. These constants as well as the observed transition frequencies are reported.