SECTIONAL TRANSACTIONS .—B. 297 
classes: (1) Reactions of the free atoms ; (2) reactions of the molecules ; 
(3) catalytic reactions in which a compound of hydrogen is the intermediate 
product effecting hydrogenation. 
In each of these cases, there are three factors which may cause the velocity 
of reaction of hydrogen to be greater than diplogen : (a) a collision factor, 
the maximum ratio being V2: 1; (6) the contribution of zero point energy 
to the energy of activation of the reaction ; and (c) the quantum mechanical 
leakage of the atoms or molecules through potential barriers, where these 
exist. 
As examples of the first class there are the mercury photosensitised 
hydrogenations of oxygen, nitrous oxide, ethylene and carbon monoxide, 
and the reduction of copper oxide. In the second class there are the 
hydrogen-chlorine and hydrogen-bromine reactions. In the third class, the 
hydrogenation of oxygen, nitrous oxide, and ethylene on a nickel surface, 
the diffusion of hydrogen through palladium, the reduction of copper 
oxide and the establishment of the equilibrium H, + D, = 2HD. 
The separation of the two isotopes does not occur in every one of these 
reactions, but in those cases where it is effected, the difference in velocities 
can, in general, be explained by the collision and zero point energy factors. 
Mr. G. B. B. M. SurHertanp.—The importance of heavy hydrogen 
in molecular physics. 
One of the outstanding problems in present-day molecular physics is 
that of determining the exact nature of the force field which exists between 
the various atoms of a polyatomic molecule. It may be approached in 
two ways. From our knowledge of the electronic structure of the separate 
atoms, we may, by using the methods of quantum mechanics, attempt to 
compute the interatomic force field. ‘The mathematical difficulties are, 
however, so great that this method is necessarily limited to a very few of 
the simplest molecules. Alternatively we may relate the constants deter- 
mining the force field to the fundamental vibration frequencies of the mole- 
cule, as determined from infra-red and Raman spectra. It happens, how- 
ever, that in general there are more arbitrary constants in the potential 
function than there are frequencies by which to determine them, so that 
one has to make some special assumption regarding the nature of the force 
field in order to reduce the number of arbitrary constants to be less than, 
or equal to, the number of fundamental frequencies. The importance of 
the new isotope lies in the fact that (for molecules containing hydrogen) 
We may replace a hydrogen atom by a diplogen one and so obtain a new set 
of frequencies which are still however related to the same set of force con- 
stants. It is therefore possible to obtain the force constants in the most 
general type of potential function without making those specific and rather 
doubtful assumptions which have hitherto been necessary. 
The structure of water and of ice has long been a matter of controversy 
in molecular physics. The advent of heavy water with its characteristically 
different physical properties should prove a touchstone whereby any theory 
of the structure of ordinary water and ice may stand or fall, since any com- 
plete theory of the structure of ordinary should enable one to predict the 
properties of the heavy water. 
Dr. L. Farkas.—Some chemical reactions of heavy hydrogen. 
The interaction D, + H,O takes place in the gas phase above 500°) Cy 
the mechanism being in principle similar to that of the H, + D, reaction. 
From catalytic experiments we have found that the equilibrium constant 
M 
