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Publication costs assisted by the National Science Foundation irans-Cyclopropane-da isomerization has been studied at low pressure as an example of a thermal, collisionally activated, competitive unimolecular reaction system. The competitive structural and geometric isomerizations have been studied in a 230-1. reactor at 480°in the pressure range near 10~3 Torr. At the lowest pressure, the ratio of the geometric to structural rate constant, kjkp, declines to kjkv ~7. The fall-off behavior is in good agreement with earlier work at higher pressures. In the presence of He bath gas, kjkp is 10% higher than for the pure substrate, when compared at identical values of kv. At low pressures the relative amounts of the competing structural and geometric processes can provide information about vibrational energy transfer on collision, although this particular system has some limitations. The kinetic expressions for this complex, reversible isomerization system are formulated. Strong collider RRKM calculations are presented.

A critical examination has been made of some aspects of the thermal decomposition of ethane and the reverse recombination reaction. The experimental Arrhenius A-factors for ethane are, in general, smaller than those which are calculated from thermodynamic quantities together with the observed rate constants for methyl recombination. Theoretical calculations also illustrate a discrepancy between the experimental work on recombination and decomposition. The experimental shapes of k/k, falloff curves and the pressure region of falloff are compared with the predictions of RRKM theory for various models.

Simple and approximate expressions of demagnetizing factors of uniformly magnetized rectangular rod and cylinder J. Appl. Phys. 66, 983 (1989); 10.1063/1.343481Simple derivation of the factor two in the Mie theory Am.An approximate form for the low pressure centrifugal effect is derived for RRKM unimolecular rate theory calculations. Comparisons are made with earlier approximations and with a more exact result. The effects on the observed activation energy and extension to the region of falloff are described.