The simple diatomic radical carbon monosulphide (CP) was detected in the circumstellar envelope of IRC+10216 by Guélin et al. and reported in 1990. The identification was made by matching 10 rotational lines observed with the IRAM 30m radio telescope.

CP and CN are pnictogenic cousins of the chalcogenic species CS and CO, respectively. Aside from differences in the masses of the heavy atoms in each diatomic, CP and CN are both open-shell species with doublet Π ground electronic states, while the ground states of CS and CO are closed-shell.