Knowledge Bank

The `$Q0$-branch lines of the $\nu 6$ fundamental band ($CH2$ wagging of the propargyl radical produced in supersonic jet by the 193 nm ArF laser photolysis was observed by time-resolved diode laser spectroscopy. Propargyl chloride diluted to 3% with 5 atm Ar was injected into an absorption cell through at 2 mm circular orifice attached to a solenoid-actuated pulsed nozzle with a reptition rate of 25 Hz. The ArF laser $(\sim 150$ mJ) was introduced to the cell from the direction opposite to the pulsed jet. Focused diode laser bean travelling through a Perry-type multireflection path crossed the supersonic jet just below the nozzle 18 times. The propargyl radical in the jet was well cooled and $\mathrm{<mrow\; data-mjx-texclass="ORD">7</mrow>}Q0$ lines with low N quantum numbers $(N=1\sim 4)$ were observed with appreciable intensities as doublets due to the spin rotation interaction. The rotational temperature of propargyl in the jet was obtained to be $16 \pm 4 $k. The time profile of absorption (decay time of about $30\mu$ sec) corresponds to the flight time of the radical across the infrared laser beam.