Differential scattering cross-sections for CN A²Π+Ar

We present the first results from a novel experimental approach to the measurement of state-to-state differential scattering cross-sections for inelastic scattering of electronically excited CN A2 ? with Ar. Photodissociation of ICN with linearly polarized 266 nm radiation generates CN X2 + (? =0, J?) with a near mono-energetic speed distribution and large anisotropy. Saturated optical pumping of the nascent CN X2 + transfers this speed distribution without distortion to selected rotational quantum states of the A2 ? (' =4) level. The products of rotational energy transfer within the A2 ? (' =4) level into the J' =0.5, F2, f, state are probed using frequency modulated stimulated emission spectroscopy on the A-X (4,2) band with a single frequency external cavity tunable diode laser. Doppler profiles of transitions from individual rotational, spin-orbit and lambda doublet specific levels are acquired for different geometrical arrangements of photolysis polarization and probe propagation directions. The resulting Doppler profiles, which for this J' =0.5 state cannot display a rotational angular momentum alignment, are combined to yield composite Doppler profiles depending on speed and translational anisotropy, which are analyzed to determine fully state-to-state resolved differential scattering cross-sections. © 2007 American Institute of Physics.