Spectroscopy of the acetylenic C-H stretch of propyne-d₃ in the region of the second overtone

The rovibrational overtone spectrum of propyne-d₃ (CD₃-C□C-H) in the region of the second overtone of the acetylenic C-H stretch (3v₁) was monitored employing photoacoustic laser absorption spectroscopy. Comparison of the observed spectrum with that simulated for a symmetric-top molecule revealed the assignment. The observed spectrum comprises the main parallel band, 3v₁, overlapped by two hot bands identified as 3v₁ + v₁₀ - v₁₀ and 3v₁ + 2v₁₀ - 2v₁₀, where v₁₀ is the degenerate C-C□C bend. The bands are resolved for the total angular momentum, allowing derivation of the parameters of the 3v₁ state and of some of those of the hot bands.