Kinetics of formation and removal of atomic halogen ions X- by HX + e- H + X- in atmospheric pressure flames for chlorine, bromine and iodine

摘要: The ions present in a variety of flames have been studied by continuously pumping small fraction the hot gases through hole and expanding it supersonically inside conical duct to low pressures required for mass spectrometric analysis. We conclude from measurements ion abundances that if halogen X is added flame containing free electrons, then negative - produced dissociative attachment forward step HX + e ⇄X +H. Reaction (I) found be rapid enough equilibrated burnt gases. This method sampling imposes drop temperature pressure on gas as expands typically there fall roughly 1400 K 99 kPa first 10 -7 s. An equilibrium such relaxes some extent these falling temperatures, but at distance around two orifice diameters expansion no further shift (1) possible. A comparison measured [X ] with one computed basis being gives quantitative measure which reaction shifts during sampling. In addition, sample often also cooled passes boundary layers immediately before entering instrument. however this effect little consequence, provided large (diameter > 0.15 mm) used. case can compared values predicted guessed velocity constants backward process one-dimensional adiabatic treatment expansion. provides rate both steps (I). magnitudes k -1 back over range 1800—2650 are 7 x -10 , 8 ml molecule s chlorine, bromine iodine, respectively (with uncertainties corresponding factors 1.6, 1.8 2.0) accordingly independent temperature. electrons has 1 its activation energy exothermicity reaction. cross-section (nor2) direction same each halogen, 1.5 -18 m 2 . From X+ M->X M not apparently occurring (M any acting chaperon) flames, we coefficient less than 3 -29 -2 three halogens temperatures 2000 K.