ON ABSORPTION SPECTRA OF ORGANIC COMPOUNDS. 231 



This was found to be true for the defines since ethylene shows a series of bands 

 in the short wave infra-red, the principal frequencies of which are exact multiples 

 uf 1-415(3 X 10'^ 



In fomiulating a theory of absorption spectra the following relationships 

 which have been established must be considered.'" 



1. Every elementary atom possesses one or more frequencies which are 

 characteristic of the element. 



2. When atoms of different elements enter into combination the resulting 

 molecule is endowed with a new frequency which is the least common multiple 

 of the frequencies of the atoms it contains. This is called the true molecular 

 frequency. 



3. The central frequencies of all absorption bands, that is, those frequencies 

 for which the absorptive power is greatest, are molecular frequencies 

 characteristic of the molecules, since these alone persist when the substaiice 

 is cooled to low temperatures. 



4. The molecular frequencies in the visible and ultra-violet regions are exact 

 multiples of a molecular frequency in the short wave infra-red, which is called 

 the infra-red fundamental frequency. 



5. The infra-red fundamental frequency either is the true molecular frequency 

 or is an exact multiple of the true molecular frequency. 



6. The breadth of an absorption band as observed at ordinary temperatm-es 

 is due to the combination of the molecular central frequency with subsidiary 

 frequencies. 



The first question which arises is the meaning of the characteristic atomic 

 frequencies which are the fundamental constants from which the whole system 

 of Irequencies shown by a molecule is derived. Presumably they are connected 

 with the shift of an electron from one stationary orbit to another, a change 

 which must require a definite amount of energy depending upon the electro- 

 magnetic force field of the atom. Indeed, it would seem that, if a possibility 

 be allowed of the shift of an electron from one stationary orbit to another, it 

 becomes necessary at once to accept the conclusion that a definite and fixed 

 amount of energy is involved in the change. It is proposed, therefore, to start 

 from this assumption, that in any elementary atom it is possible to shift an 

 electron from one stationary orbit to another, that a definite amount of energy 

 is required to effect the change, and that this fixed quantity of energy is 

 connected with the frequency by the relation — 



Fixed Quantity of Energy _, 



T^i 3-— r =^ = frequency. 



Constant 



This is readily to be understood if the constant involves a function of the time 

 taken in the actual operation, which is the same for every atom and is a universal 

 constant. 



This elementary quantum of energy involved in the electron shift is without 

 doubt the basis of the whole energy quantum hypothesis as applied to absorption 

 and radiation, for it can be shown that the whole can be built up from the 

 original assumption of the elementary quantum as a specific property of the 

 atom. For the .sake of convenience only it will be necessary to make use of a 

 value for the constant, and the most recent value for this, based on Planck's 

 theory, is 6-56 x 10"^'. Using this value, the elementary quanta already 

 calculated, namely, those of hydrogen, oxygen, and sulphur, lie between 

 5-25 X lO'io and 1-65 x 10"'* erg, corresponding with frequencies between 

 8-19 X 101" and 2-54 x 10". 



The difference between this conception and Planck's theory may be 

 emphasised. Whereas according to the latter the frequency is accepted as a 

 characteristic of the atom and the quantum is the result of discontinuous 

 absorption or emission at that frequency, the present theory assumes the quantum 

 of energy as being due to a specific process taking place in the atom and hence 

 a fundamental characteristic of the atom, and that the frequency exhibited by 

 the atom is established and determined by that process. The present theory, 

 therefore, gives a simple physical basis to the energy quantum. 



