A system of physical chemistry - Index of

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A system of physical chemistry - Index of

198

A SYSTEAl OF PHYSICAL CHEMISTRY

Physik, 40, 473. (191 3)) Js also, according to Kriiger, to be referred to

precessional vibrations, which are obeying the quantum principle of

energy distribution as a function of temperature. Kriiger's conclusions

may be summed up as follows :—

Since, in general, we may expect all molecular systems to possess

rotating electrons, we may say that in the case of molecules which

contain two or more atoms such molecules do not exhibit rotation as

a whole, but on the other hand exhibit precessional vibrations on account

of their gyroscopic properties. The number of degrees of freedom

on this view remains the same as on the older view of rotations.

It has already been pointed out that the molecular heats lead us

to the conclusion that in the ordinary range of temperature a diatomic

gas has five and not six degrees of freedom. That is, one of the expected

degrees is missing. Kriiger points out that the ordinary rotation theory

does not give any satisfactor)' explanation of why there is one degree of

freedom missing. By making use of the precessional vibration idea

the fact that five degrees are possessed is self-evident, for precessional

vibration gives rise to two degrees of freedom (purely kinetic), and

the free translation of the molecule gives rise to three degrees of

freedom also purely kinetic. It will be observed that Kriiger is

not considering the vibration of the ordinary kind of the two

atoms with respect to one another. Further, in the case of a monatomic

gas we have seen that the inertia terms A and C approximate

to one another with the result that the frequency of precession

becomes exceedingly great, and in the limit when the molecule is

spherical it becomes infinite. Hence monatomic molecules are unable,

according to the quantum theory, to take up any sensible amount of

energy over the temperature ranges hitherto examined, for the only

kind of radiant energy which such a system would be capable of picking

That is,

up would be that belonging to the extreme ultra-violet region.

the monatomic gases, such as mercury, argon, etc., do not possess any

the mole-

internal energy as far as their molecular heats are concerned ;

cular heat is completely taken account of by the three degrees of freedom

of translation of the molecule as a whole. This explanation of the

behaviour of monatomic gases is one of the main advantages of Kriiger's

theory.

In the second of the papers cited Kriiger goes on to consider in

more detail the question of the infra-red spectra of gases in relation to

the concept of precessional vibrations.

It has been shown experimentally by Rubens and Wartenberg

{Verh. D. phys. Ges., 13, 796 (191 1)) that the elementary gases such

as H2, O2, CI2, Br2, which are electrically neutral structures, show no

absorption in the infra-red region between 23 and 314/x, whilst on the

other hand the markedly electrically-polar gases, such as HCl, HBr,

and H2O, possess strong absorption over this range. This fact has

hitherto been ascribed to the rotations of the dipoles, for rotating dipoles

must emit and absorb radiant energy.

model as extended by W. Kossel {Ann.

According to Bohr's atomic

Fhysik, 49, 359 (191 6)), these

fl

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