Drift velocities of low energy electrons have been measured in CH4, C D 4 , SiH4, SiD4, C2H6, C3H8, C2H4, C2H2, C2D2, CH3C1, AsH3, CH3COCCH3, CH30CH3, C~HSOH. The results are interpreted in terms of energy transfer from the electrons to rotational or vibrational modes of the molecules.Measurements on electron swarms 1 9 2 and low-energy electron beams 3 have shown that inelastic collisions are possible between slow electrons (i.e., electrons of insufficient energy to cause electronic excitations) and polyatomic molecules. Two processes occurring may be rotational or vibrational excitation of the molecule. Theoretically,4 neither of these can take place " directly '' because of the low electron : molecule mass ratio. Rotational excitation can, however, take place with a high probability in polar 5 or quadrupolar 6 species, where the interaction between the molecule and a distant slow electron is sufficiently great for rotational excitation to be effected. Vibrational excitation is less easily understood. Indirect excitation of some species is possible by a kind of resonance scattering, as Schulz 3 has suggested for nitrogen.N2+e-+[N;]-+N2+e. In such a process, the energy required by the incoming electron depends on the relative positions of the potential energy curves of the parent molecule and the intermediate negative species. For nitrogen, the excitation cross-section is maximum at 2.3 eV while the vibrational quantum is 0.3 eV. However, in some gases, there is evidence of large energy losses by electrons of energy in the region of one vibrational quantum-losses which appear too great to be accounted for by rotational excitation.1' 2 In this study, by looking at slow electron drift velocities in a number of polyatomic gases, we hoped to determine whether or not vibrational excitation of polyatomic molecules is caused by low-energy electrons. EXPERIMENTALDrift velocity measurements were made in an electron shutter apparatus, based on that originally used by Bradbury and Nielson,7 and modified by Phelps 8 et al. In the present system, photoelectrons, ejected from a cathode by a u.-v. beam from a mercury vapour lamp, were drawn upwards by an electric field and collected on the anode. The electric field was maintained uniform by a series of guardrings, GI, G3, G4, G5. The electron shutters, G2 and Gg, each consisted of a plane grid of parallel wires, alternate wires of which were connected together. Application of a square-wave potential to the wires caused each shutter to open and shut to electrons periodically. The waves applied to G2 and Gg were exactly in phase. The electron current reaching the anode depended on the frequency with which the shutters opened and shut, being maximum when the frequency was given by llf = d/nW, where d is the distance between G2 and Gg, Wis the electron drift velocity, and n an integer.

The effect of molecular interaction at high pressure has been discussed using the approximation that a molecule enclosed by its neighbours may be considered t o be in a box with an infinitely steep potential wall. Tbe calculation has been carried out by the variation method for the hydrogen molecule-ion in a spheroidal box, and the results have been compared with earlier calculations on the hydrogen atom in a spherical box, with a cruder calculation for diatomic molecules, and with experimental results on other gases. The approximation apparently gives results of the correct order of magnitude, but tends to exaggerate the effect of pressure.

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The thermal decomposition of nitromethane has been studied by a static Eethod over the range 380-430° C, and shown t o be a homogeneous reaction, of approximately first order at pressures between 200 and 400 mm., with a rate constant given by k = 1014-6 exp (-53,60o/RT) sec.-l.The main produch are nitric oxide, methane, carbon monoxide and water, with some carbon dioxide, and small quantities of ethane, ethylene and nitrous oxide. The initial step is considered t o be CH,N02 + CH, + NO2, followed by a non-chain radical mechanism. C-N bond in nitromethane is thus estimated t o be 53 kcal.

The second virial coefficients of equimolecular mixtures of carbon dioxide with nitrogen, oxygen, carbon monoxide, argon and hydrogen have been measured at 30°, 60" and 90" C. For all these mixtures the derived values of the interaction virial coefficient BIZ are not very different from those calculated using the empirical combining laws for the force constants in the Lennard-Jones potential, but are appreciably less dependent on temperature.I n calculating the coefficients of interaction between mixtures of non-polar gases, empirical combining laws are used to relate the force constants between unlike molecules to those between like molecules.