Separation of O, C, and S isotopes by twohyphen;step, laser photodissociation of OCS

摘要

Isotopes of O, C, and S have been separated by twohyphen;step, laser photodissociation of OCS. The technique utilizes isotopically selective vibrational excitation of OCS in the ngr;2(bending) vibrational mode with a linehyphen;tuned CO2laser (lgr;sim;9.4 mgr;m), followed by photodissociation with a KrF excimer laser (lgr;=249 nm) and chemical scavenging of the sulfur atoms. Enrichment factors ranging from 1.5 to 3.5 were obtained for different isotopes. A sensitive IR absorption apparatus was used to measure absorption of the high energy CO2laser pulse by OCS as a function of pressure and laser fluence. Average absorptions ranging up to 1.5 photons/molecule were attributed to rapid rotational relaxation and in part to sequential absorption up the ladder of ngr;2vibrational levels. The 249 nm photodissociation cross section of OCS was measured as a function of absorbed IR energy. An excitation of one CO2laser photon per molecule, or two quanta of ngr;2vibration per molecule, increased the photodissociation cross section by a factor of 9 over the thermal (295 K) cross section. A rate constant of (4.8plusmn;1.0)times;105sminus;1thinsp;Torrminus;1was inferred for the exchange of ngr;2vibrational energy between isotopic varieties of OCS.