Time-resolved diode laser spectroscopy of the ν6 band of propargyl produced by the UV photolysis of allene

Abstract

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 ν6 (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), εaa=−0.017 58(95), and εbb=−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 ν6 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 ΔK centrifugal distortion constant are accounted for by the a-type Coriolis interaction between the ν6 and ν10 states, where ν10 is the CH2-rocking vibration.