Time-resolved diode laser spectroscopy of the v₆ band of propargyl produced by the UV photolysis of allene

The propargyl radical (CH₂C≡CH) produced by the ArF excimer laser photolysis of allene was observed by time-resolved infrared diode laser spectroscopy. More than one hundred and fifty absorption lines have been assigned to the v₆ (CH₂-wagging) fundamental band of propargyl. Most of the absorption lines were observed as doublets due to the spin-rotation interaction in the ²B₁ ground electronic state. The rotational and spin-rotation interaction constants derived for the ground vibrational state are, A₀ = 9.608 47(36), B₀ = 0.317 674(24), C₀ = 0.307 098(24), ∈_aa = -0.017 58(95), and ∈_bb = -0.000 355(76) cm^-1, where the figures in parentheses are 2.5 times standard deviations to be attached to the last digit. The v₆ band origin is 687.176 03(62) cm^-1, consistent with the infrared spectrum observed in the argon matrix. Anomalously large vibrational changes in the A rotational constant and the Δ_K centrifugal distortion constant are accounted for by the a-type Coriolis interaction between the v₆ and v₁₀ states, where v₁₀ is the CH₂-rocking vibration.