High temperature flowing afterglow

Figure A3.5.5. Rate constants for the reaction of Ar with O2 as a fiinction of temperature. CRESU stands for the French translation of reaction kinetics at supersonic conditions, SIFT is selected ion flow tube, FA is flowing afterglow and HTFA is high temperature flowing afterglow.

Figure 1. Schematic drawing of the high temperature flowing afterglow (HTFA).

Figure 2 Rate coefficients for the reaction of Ol with methane measured as a function of average kinetic energy at several temperatures in a variable-temperature selected-ion flow drift tube (VT-SIFDT). Also shown are data taken with a high-temperature flowing afterglow (HFTA) and a drift tube. Reproduced with permission from Viggiano AA and Morris MA (1996) Journal of Physical Chemistry 100 19227-19240.

Flierl P M ef a/1996 Flowing afterglow apparatus for the study of ion-molecule reactions at high temperatures Rev. Scl. Instrum. 67 2142-8... 

Fig. 15. Sodium charge transfer cross sections with atmospheric molecular ions as measured using the high temperature guided-ion beam experiment (circles). Triangles are the flowing-afterglow measurements by Farragher et and squares are the...

The HTFA is in practice operated like a typical flowing afterglow of which the principles have been reported in detail elsewhere.A detailed description of the Air Force Research Laboratory flowing afterglow apparatus is found in Ref. 22, so only the key aspects and recent modifications will be discussed here with emphasis on the particular problems associated with high temperature measurements. The remainder of the section outlines how the HTFA data are combined with other measurements to derive internal energy dependencies. 

The flowing afterglow (FA) is a flow reactor tube. Ions are produced by an ion source at the upstream end of the tube. These ions are carried by a buffer gas (He or Ar) and thermahzed to room temperature down the flow tube. On their way down, they react with neutral molecules added downstream in the tube. The (ionic) reaction products can be moiutored in a number of ways, including optical spectroscopy and MS. In the latter case, the resulting swarm of ions is sampled through an orifice into a high-vacuum chamber where they are mass analyzed and detected. 

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