METHYL RADICAL MEASUREMENT BY CAVITY RING-DOWN SPECTROSCOPY

Cavity ring-down spectroscopy has been used to measure the absorbance of methyl radicals near 216 nm. The methyl radicals are generated by a hot tungsten filament heated to 2300 K in a mixture of 0.5% CH4 in H- 2 slowly flowing through the reactor at 20 Torr total pressure. CH3 ab sorbances are detected with a noise-equivalent sensitivity of two part s in 10(5) using a narrow pencil of UV light 0.5 mm in diameter, which allows measurement of spatial profiles of CH3 for column densities of 3 x 10(12) radicals/cm(2) (3 x 10(12) radicals/cm(3) x 1 cm absorptio n pathlength).