The isotopic composition of a multiatomic isotope-bearing species such as CO.sub.2 in an analyte is measured by maintaining the analyte in a condition such that isotope-bearing species are present in an excited state and directing light at wavelengths corresponding to transition energies...http://www.google.es/patents/US5783445?utm_source=gb-gplus-sharePatente US5783445 - Methods and apparatus for isotopic analysis
