The work presented in this thesis concerns the electronic excitation of the molecule NaK by circularly polarized laser light. The subsequent fluorescence is analysed to obtain the circular polarization of the emission and the cross-sections for collisionally induced rotational quantum jumps. The degree of circular polarization, C, of the emission may be used as a measure of the extent to which a molecule undergoes reorientation during a collision. The intermolecular potential for the collision NaK-rare gas atom is probed by observing the rotational 'propensities' (favoured energy transfer channels) from two excited states. The D ITT state was excited by an argon ion laser, the C 'IT state by a R6G tunable dye laser. The tunability available within the c'IT manifold enabled the author to study the variation of C with the value of the initially excited rotational level, under rotationally elastic conditions. The values of both C and of the cross-sections for collisiona11y induced rotational energy transfer were also obtained as a function of the excited rotational level. The results indicate that reorientation of a heteronuclear diatomic during collisions with rare gas atoms is very dependent upon the intermolecular potential and d~~ics during the encounter.