The intersystem (a^{3} \Pi-X^{1} \Sigma^{+}(0,0)) transition of (\mathrm{CS}) has been recorded by means of Fourier transform spectrometry from a hot cathode, low-pressure emission source. Study of the relative line intensities in the three subbands shows interference effects appearing (i) between parallel and perpendicular transition moments, causing the (P) branches to be much weaker than the (R) branches (the ratio (\mu_{|} / \mu_{\perp}) has been determined to be 0.14 ), and (ii) between different parallel transition moments, so that the average intensity of the subband involving the (\Omega=0) component is smaller than that predicted from a simple model. The intensity ratios (\left./{ }^{3} \mathrm{II}{0^{-}}{ }^{1} \Sigma^{+}\right) /\left({ }^{3} \mathrm{II}{1^{-}}{ }^{-} \Sigma^{+}\right))and (/\left({ }^{3} \mathrm{II}{2}-\right.) (\left.{ }^{1} \Sigma^{+}\right) / I\left({ }^{3} \mathrm{II}{1}-{ }^{-} \Sigma^{+}\right)), which are, respectively, 0.02 and 0.00 in the absence of rotation, increase to 0.08 and 0.04 in the rotating molecule. Reassignment to the three ({ }^{3} \Pi_{\mathfrak{k}}) substates of the fluorescence lifetimes observed in solid phase was necessary as a consequence of the intensity measurements made in the present work. (c: 1994 Academic Press. Inc.