The present invention relates to a process and to an apparatus for determining molecular spectra in unseparated mixtures of different molecules, particularly in molecular isotopic mixtures.
It is known that photochemical isotopic separation can be carried out using laser light. Information concerning the exact wave lengths at which the isotopes which are to be separated absorb, is extremely important for the economy of such a separation process. Heretofore two possibilities of finding these wave lengths have existed;
(a) The separation process is carried out using various wave lengths and these are varied until by chance there results an optimum separation. The wave lengths are determined by estimating the isotope shift, that is, the shift of maximum absorption, which shift results from an isotope substitution in respective molecules in comparison with other molecules which are to be separated therefrom. An optimisation of this kind by varying the actual separation process itself is time-consuming and also costly. For this reason, only a very small area of the complex molecular absorption spectrum can be examined and consequently the chance of finding an optimum wave length is small.
(b) where separate samples of isotopes are available the absorption spectra of the individual isotopes can be measured. In a few cases, such spectra can be found in the literature. A comparison of the spectra then yields the optimum wave length to be used for a separation process. This method is, however, restricted to molecules, whose isotopic spectra are either already known or else whose isotopic spectra can be obtained if they can be separated into their isotopes by means of methods other than photochemical methods. The use of other conventional separation methods which enable separation by means of the differing mass of isotopes fails however with large molecules, particularly if various types of isotopes of the same weight (isotopomers) exist. In addition, the chemical synthesis of specific molecules which are substituted with isotopes is extremely difficult and only in rare cases does this lead to a complete separation.