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The study of collisional transitional probabilities for the de‐excitation by inert gases of chemically activated sec‐butyl radicals, excited to internal energies in excess of 40 kcal mole−1, has been extended to H2, D2, N2, CO2, CH4, CD3F, CH3Cl, and SF6. The diatomic gases display behavior similar to the rare gases, and on a preferred exponential model of collisional transition probabilities the average amount of energy transferred per collision is 〈ΔE〉expon≃1.3 kcal mole−1. On a stepladder model the corresponding amount is ΔE≃2.5 kcal mole−1. From higher‐pressure data, the efficiency for CD3F, CH3Cl, and SF6 is deduced to be comparable with that for butene and, on a preferred stepladder model, ΔE>9 kcal. For CO2 and CH4 the behavior is intermediate. The possible importance of the role of internal rotation of butyl in facilitating energy transfer is noted; some uncertainty concerning the role of over‐all rotations and vibrational modes of the deactivator in the relaxation process exists.

Vibrationally excited sec‐butyl radicals, having a narrow range of energies above 40 kcal mole−1, were produced in a heat bath of cis‐butene‐2‐rare‐gas mixtures by H addition to cis‐butene‐2. He, Ne, Ar, and Kr were used. Two competing reactions of the chemically activated radicals, decomposition by C–C rupture with critical energy of 33 kcal mole−1 and collisional stabilization, were studied as a function of pressure. Apparent rate constants for decomposition ka were obtained at three temperatures over a range of bath pressures by analysis of the decomposition and stabilization products. Strong and weak multistep collisional deactivation processes, corresponding to transfer of all or only part of the initial excess vibration energy (≥7 kcal mole−1) of the radicals, were considered. Multistep models of various step sizes (ΔE) give a family of calculated curves of ka as a function of p, each of which turns up from a quasi‐constant value at higher pressures to higher values at low pressures. Comparison with...