ON ABSORPTION SPECTRA OF ORGANIC COMPOUNDS. 239 



which will result in the establishment of the infra-red fundamental 

 5'04 X 10'^. Since one quantum at this frequency equals the sum total of 

 energy evolved, the absorption of one energy quantum at this frequency will 

 result in the molecule just being resolved back again into its atoms. 



The next stage in the process will be the formation of the molecular force 

 field, and let this be accompanied by the loss of 20 quanta at the infra-red 

 fundamental 5-04 x lO^". As shown above, the molecular system will now be 

 endowed with an additional characteristic frequency, 5-04 X 21 X 10'^ or 

 1-0584 X 10'*, which lies in the ultra-violet region of the specti-um. The energy 

 lost by each molecule during the condensation of its force field will be 

 504 X 20 X 6-56 x 10"'* or 6-61248 X lO''^ ergs. The total energy therefore 

 evolved in the two processes is the sum of 3-30624 x 10"'^ ergs evolved in the com- 

 bination of the atoms and 6-61248 x 10"'^ ergs evolved during the condensation to 

 form the molecular force field, which amounts to 6"943104 X 10''^ ergs. This 

 amount of energy, however, is equal to one qua-ntum at the frequency 

 1-0584 X 10'^, which is characteristic of the molecular phase. As this is obvi- 

 ously true whatever may have been the number of quanta at the infra-red 

 fundamental lost during the formation of the molecular force field, the general 

 conclusion is reached that one energy quantum measured at the largest fre- 

 quency characteristic of the molecule is just sufficient to resolve that molecule 

 into its atoms. This is a general conclusion which includes Einstein's photo- 

 chemical la-sv. 



The values taken above of atomic frequencies,* infra-red fundamental, and 

 molecular phase frequency closely approximate to those observed with many 

 compounds. It will be seen that the amount of energy evolved in the com- 

 plete process may be very large, and for a gram-molecule amounts in the above 

 instance to about 102,320 calories. It must, of course, be remembered that in 

 any reaction the observed heat evolved is less than tlie total amount evolved 

 in the formation of the molecular systems of the products by the amount 

 necessary to resolve the initial substance or substances into atoms. 



An important deduction from this molecular phase theory may be made as 

 regards the energy changes involved in chemical reaction. It is obvious that 

 in any reaction in which the first stage is the resolution of the molecule into 

 ite atoms the energy necessary for this first stage can at once be found from 

 the frequency of the phase in which that molecule exists. Unfortunately, 

 there does not seem to be known at present a single instance of a simple 

 reaction in which the molecular phase frequencies have been accurately 

 measured, both for the original substance and the products, and consequently 

 it is not possible at the present time accurately to calculate the net change of 

 energy observed in any reaction. On the other hand, in the vast majority of 

 chemical reactions the reacting molecules are not resolved into their atoms in 

 the first stage of the larocess. It has been shown in a number of cases that it 

 is only necessary to bring the molecules into a particular phase in order to 

 enable them to enter into the desired reaction. A very typical example of the 

 difference in reactivity shown by the different molecular phases of the same 

 molecule is afforded by benzaldehyde. In alcoholic solution this substance ex- 

 hibits two molecular frequencies in the ultra-violet, and therefore two mole- 

 cular phases co-exist. It is well known that in alcoholic solution benzaldehyde 

 is readily oxidised by gaseous oxygen to benzoic acid, and that it is not con- 

 verted to benzaldehydesulphonic acid when sulphuric acid is added to the 



* In the example given simple numbers have been used for the atomic fre- 

 quencies in order to avoid complexity in calculation. It is perhaps worth 

 while to_ point out here that there are certain indications that the fundamental 

 frequencies of the atoms of different element.^ are possibly connected by simple 

 arithmetical relations. A sufficient number of these atomic frequencies has not 

 yet been computed, owing to the dearth of accurate measurements of the 

 subsidiary frequencies of simple molecules, to justify any conclusioas being 

 made. It is of some interest, however, to note that in sulphur dioxide the 

 oxygen frequency 2-4531 x 10" is almost exactly three times the sulphur 

 frequency 8-19 x 10>o. and that in the case of the water molecule the atomic 

 frecjuenry 2-11.59 x 10" is very nearly twice the atomic frequency 1-0635 x lO'V 



