Hypoosmotic shock kinetics of the normal human red cell (25 degrees C) were investigated by means of a rapid kinetics apparatus, with a resolving time of about 50 ms. The results are compared with some current models for hemolysis. The fast hemolysis plots are not true symmetric sigmoids, in contrast to results from less stressful conditions, nor can they be simply fitted to an "all or none" process. In the most severe conditions, mixing with neat water, the velocities with which red cells start to hemolyze depend on the rate at which the cell is converted to a swollen sphere (lag phase). Under such conditions, the mean time to rupture and start of leaking is about 0.6 s. The rate of osmotically driven solvent flow is probably the principal controlling factor in the discocyte to sphere transformation. The overall course of hemolysis can be described in terms of two rate processes and a distribution of cell fragilities. The fragilities probably depend on the age of individual cells in the samples. In the low-salt region, the effect of hypotonicity as well as hypoosmolality is discerned. The surface charge on the red cell provided no driving force for rupture above salt concentration 0.10M, but at 0.05 M salt and below, electrostatic effects may contribute.

The absolute rate constant for the reaction OH + CH3CCl3 → H2O + CH2CCl3 has been determined by the flash photolysis resonance fluorescence technique from 253 to 363K. The results are used to recommend the Arrhenius expression in units of cm³ molec−1s−1. Use of this equation with atmospheric observational data on methyl chloroform nearly doubles the predicted tropospheric OH reaction sink strength for the removal of important atmospheric gases whose lifetimes are controlled by OH. Comparison of the results reported here with previously reported literature values indicates a strong interference of olefinic impurities on the past investigations.

The flash photolysis resonance fluorescence technique has been used to reinvestigate the kinetics of the oxygen atom-oxygen molecule combination reaction. Third-order rate constants for 02, N2, and Ar as deactivant molecules were determined over the temperature range of 219-368 K. The results presented herein are the most extensive data sets available for atmospheric modeling and are used to formulate a recommendation for such purposes. The recommended rate expressions are k p = (1.07 X exp(525/T) cm6/molecule2 sec or hair --(6.3 X 10-34)(T/300)-1.9 cm6/molecule2 sec Comparisons of these results with existing literature data are presented.

The flash photolysis resonance fluorescence technique was employed to investigate the rate constant for the reaction Cl + CH20 -»• HCI + CHO from 223 to 323 K. An Arrhenius fit of the data gives ki = (1.09 ± 0.40) X 10"10 exp[-(131 ± 98)/T] in units of cm3 molecule'1 s'1. The results are compared to two very recent kinetic studies and are assessed in view of the reaction's role in disrupting the Cl-CIO stratospheric ozone depletion chain.

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