Knowledge Bank

A tunable dye laser was used to excite $K2$ from the ground $X(1\Sigma g+)$ state into the continuum of the $B(1\Sigma u)$ state. This results in dissociation of the molecule producing an excited $K\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}P3/2$ atom which fluoresces. By monitoring the atomic $D2$ fluorescence under these molecular beam (collision-free) conditions, we were able to measure the pure bound-free absorption profile. At the same time, the polarization of the atomic fluorescence was measured for different laser excitation frequencies. We believe this to be the first observation of a large variation in the polarization, ranging from $15\pm 2\%$ to $-6.3\pm 0.4\%$ as a function of laser excitation wave-length. The results are explained a) using the theory of Van Brunt and Zare1, which predicts a maximum polarization of 14.3% (axial recoil) and a minimum of -7.7% (transverse recoil) and b) the Rotating molecule $theory2$ where the polarization is a function of the angle of rotation of a half collision. Classical, semiclassical and quantum-mechanical calculations in the $K2$ case were also performed and a comparison with the experimental results is given.