Knowledge Bank

The $10.1\leftarrow O0.0$ rotational spectrum of the propargyl radical $(CH2C-CH)$ was observed by a Fourier-transform microwave spectrometer with pulsed discharge nozzale. The propargyl radical was produced by dc discharge $(\sim 1.3$ kV. 200mA) of propargyl chloride $(ClCH2C-CH)$ diluted to 0.25% with 5 atom Ar (0.25%) and injected into an absorption cell through the pulsed nozzle with the repetition rate of 5 Hz. The rotational temperature of the propargyl was estimated as low as a few K. The rotational transition. $10.1\leftarrow O0.0$. Observed was splitted into twelve components due to the electron spin-rotation interaction ($J=0.5\leftarrow 0.5$ and $1.5\leftarrow 0.5$) and the hyperfine interaction because of the three H nuclei (I = 0.5). The rotational, centrifugal distortion, and spin-rotation constants for the ground state, $A=288045.5(34),B~=9365.2766(73).B-C=316.30(23),\epsilon aa-544.2(29),\epsilon bb=-11.043(037)$, and $\epsilon cc=-1.0$(fixed) MHz, as well as the hyperfine interaction constants, of $\alpha F,T00$ and $Tbb$, for both the acetylenic (I=0.5) and methylenic (I=1) protons were derived from the MW spectrum combined with the infrared diode laser spectra of the $v6$ fundamental band (1).The dipole moment of the propargyl radical is estimated to be less than 0.2 D from the microwave power dependence of the spectrum, which ageress with the recent ab initio calculation, 0.14 D (2). The figures in parentheses are standard deviation to be attached to the last digit.