Knowledge Bank

The $\nu 6$ ($CH2$ wagging) fundamental band of the propargyl radical ($CH2C=CH$) was observed by time-resolved infrared diode laser spectroscopy. The propargyl radical was produced by the photolysis of allene $(C3H4)$ or propargyl chloride ($ClCH3C-CH$) with 193 nm ArF excimer laser light. More than 120 absorption lines have been assigned to the $v6$ fundamental band of propargyl including $Ka=1\leftarrow 0,0\leftarrow 1,2-1,1\leftarrow 2$, and $3\leftarrow 4$ subbands. Most of the absorption lines were observed as doublets due to the spin-rotation interaction in the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B1$ ground electronic state. The rotational and spin-rotation constants for the ground state. $A=288045.5(34),B~=9365.2766(73),B-C-316,30(23)\epsilon \infty -544.2(29),\epsilon bb-11.043(37)$, and $\epsilon \infty =-1.0$ (fixed) MHx, are derived from the diode laser spectrum combined with the $10.1\leftarrow O0.0$ rotational spectrum by FTMW spectroscopy (1). The vibrational band origin obtained is $687.174.89(63)cm-1$, which is consistent with the infrared spectrum observed in the argon matrix (2). The molecular constants for the $\nu 6$ state are largely affected by the $\alpha$-type Coriolis interaction with the $v10(CH2$ rocking) vibration, for example, the rotational and the centrifugal distortion constants A and $\Delta k$ in the $v6$ state change by $-13440(23)$ and $-24.2(21)$ MHz, respectively, from those of the ground state. The figures in parentheses are standard deviation to be attached to the last digit.