The microwave spectrum of C1ONO2 has been analyzed in the laboratory under high resolution. Rotational constants are reported for the ground and lowest vibrational states of the 35Cl and 37Cl isotopic forms. From Stark effect measurements the electric dipole moment was found to have components along two principal axes, &mgr;a=0.72¿0.10 Debye and &mgr;b=0.28¿.04 Debye. Difficulties encountered in handling gas phase samples of ClONO2 are discussed in some detail and evidence is presented for the existence of a closely related chlorine containing compounds which is believed to be ClONO. This second compound may also prove to be important in detailed atmospheric modeling. The rotational constants for ClONO are also given.