Emission spectrum for polar super rotors in a cold buffer gas

Rate coefficients for cold and ultracold He+CO collisions are used together with radiative lifetimes to investigate the relaxation of rotationally hot polar molecules in the presence of a cold or ultracold helium buffer gas. Starting with an initial Gaussian distribution of highly excited rotational states, such as might be produced by an optical centrifuge, the time-dependent relaxation of a collection of super rotors is studied and in the case of CO an emission spectrum which contains the collisional information is predicted as a function of buffer gas density. Implications for the experimental detection of cold and ultracold quasiresonant atom-diatom scattering is discussed.