An improved singlet oxygen generator (SOG) and method of using gas phase electronically excited states of oxygen for bio-medical and chemical treatment applications are disclosed. According to the invention, both gas phase O.sub.2(.sup.1.SIGMA.) and O.sub.2(.sup.1.DELTA.) are used for medical treatment, sterilization, and deactivation of biological and chemical agents, including diseased tissue and biological and chemical weapons. The improved SOG is compact and scalable, portable, capable of operating in a zero-gravity or low gravity environment, may use gaseous diluent or buffer gas, and is capable of operating at pressures as high as one atmosphere. The SOG is capable of operating within a short distance of the target site for the electronically excited states of oxygen, which are delivered to the target site via a conduit. The SOG and delivery system provide higher yields of electronically excited oxygen with longer lifetimes suitable for bio-medical applications.