Determination of the absolute Raman cross section of methyl

Methyl (CH3) is generated by photodissociation of methyliodide (CH3I) applying an excimer laser operating at 248 nm. The CH3 is detected using 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 measurements yield a Raman cross section of dσ/dΩ = 7 × 10−31 cm2/sr at λP = 532 nm.