title: Ultrasensitive detection of atmospheric constituents by supersonic molecular beam, multiphoton ionization, mass spectroscopy.
abstract: An ultrasensitive detection method for atmospheric monitoring has been developed based on the technique of supersonic molecular beam, resonance enhanced multiphoton ionization, and time-of-flight mass spectroscopy (MB/REMPI/TOFMS). Several organophosphonate and organosulfide compounds, representing simulants to a class of toxic compounds, were studied. Detection levels as low as 300 ppt (dimethyl sulfide) were obtained. Single-vibronic-level REMPI of the cooled molecules in conjunction with TOFMS provided selectivity of ~10(4) against chemically similar compounds in humid air expansions. The fragment ions formed by REMPI excitation are shown for diisopropyl methylphosphonate to depend strongly on the resonant intermediate state of the neutral molecule.
authors.forename: J A
authors.initials: JA
authors.lastname: Syage
authors.forename: J E
authors.initials: JE
authors.lastname: Pollard
authors.forename: R B
authors.initials: RB
authors.lastname: Cohen