Methyl (CH3) is generated by photodissociation of methyliodide (CH3I)
applying an excimer laser operating at 248 nm. The CH3 is detected usi
ng coherent anti-Stokes Raman spectroscopy (CARS). The CH3 density is
deduced by monitoring simultaneously the reduction of the CARS signal
of the parent molecule CH3I. CARS spectra of CH3 (v = 3005 cm(-1)) are
recorded and the rotational temperature is evaluated. The CARS signal
intensities are compared with those of deuterium and methane in order
to obtain an absolute calibration of the Raman cross section. The mea
surements yield a Raman cross section of d sigma/d Omega = 7 x 10(-31)
cm(2)/sr at lambda(p) = 532 nm.