The reaction of CH, + C1, produces predominantly CH3CI + HCI, which above 1200 K goes to olefins, aromatics, and HCI. Results obtained in laboratory experiments and detailed modeling of the chlorine-catalyzed polymerization of methane a t 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride.

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Experimental rate data for some radical-radical and some atom-molecule reactions are quantitatively accounted for by a proposed model in which the preferred reaction path, with high rate constants, is recombination followed by stabilization or a chemically activated concerted decomposition. When the energetics prohibits such pathways, the metathesis with lower reaction cross sections remains the significant one. The selected pathways and log k (L/mol s) values which were obtained for Cl + H02 and HC1 + 0 are presented. H02 + Cl HC1 + 02(1)stratosphere by trapping Cl as HC1.1 Several experi-ments1-5,9 have been conducted to measure its kinetic parameters. The reported values found for log ¿x (298) of 10.3 ± 0.4,210.2 ± 0.2,910.6 ± 0.1,310.4 ± 0.2,4 5and 10.6 ± 0.21 L/(mol s) seem to be higher than even the effective collision frequency (log Z ( = 1.7 Á) = 10.2 L/(mol s)).

The magnetic susceptibility of photodissociated carbon monoxy myoglobin has been measured over the temperature range from 1.7 to 25 K at 10 and 50 kG with a superconducting susceptometer. The spin and the crystal field parameters of the iron ion were extracted by a spin Hamiltonian approach. Under equivalent conditions the magnetic susceptibility of deoxy myoglobin was measured. In both experiments the CO-bound protein was used as a diamagnetic reference. Above about 5 K the metastable photolysed state and the equilibrium deoxy form of myoglobin are magnetically indistinguishable and can be fitted with S = 2 and g = 2. The transition from spin 0 to spin 2 and the conformational changes known to accompany the electronic change thus also occur after photolysis at low temperature. At temperatures below 5 K, differences become apparent, indicating a somewhat smaller zero-field splitting in the photoproduct as compared to the ligand-free state at equilibrium. In qualitative agreement with observations made by other techniques, the data imply that even at 1.7 K substantial structural relaxation occurs in the heme region of myoglobin after photodissociation. The results are important for the interpretation of the ligand binding kinetics after flash photolysis at low temperature and contribute to the understanding of the relationship between electronic structure and function in heme proteins. Heme proteins perform a wide variety of functions, from oxygen storage to detoxification. Since they all share the same prosthetic group, a detailed understanding of the function of one heme protein can provide insight into a broader field. The binding of small ligands such as dioxygen and CO to ferrous Mb and Hb is probably the simplest such biological process and it has been studied with a variety of tools (1-4). Flash photolysis experiments over a wide range of time and temperature have established that the controlling reaction in ligand binding occurs at the heme group and involves the heme iron (5, 6). In the discussion of the crucial association and dissociation step it is generally assumed that the ligandfree (deoxy) form of the ferrous heme is in the high-spin state (S = 2) while the ligand-bound form is in the low-spin state (S = 0). Consequently, association and dissociation of 02 and CO are assumed to be accompanied by a spin change of 2.The assignment of the spin states is based on the pioneering magnetic susceptibility measurements of Pauling and Coryell (7) on Hb and related proteins. MbCO was shown to be diamagnetic by Theorell and Ehrenberg (8). The magnetic properties of deoxy Hb and Mb have been studied by Nakano et al. (9). In addition to verifying the spin state they characterized the electronic fine structure of the iron in these heme proteins.Ligand binding not only modifies the electronic structure of the heme iron but also induces distinct changes in the conformation of the heme and its environment (10). X-ray crystallography shows that in deoxy Mb (11) the iron ion lies out of the mean heme plane by...