Photochemical enrichment of the chlorine and carbon isotopes induced in Freon (CF₂Cl₂) by CO₂ laser pulses

Enrichment of the carbon isotopes by photodissociation or photochemical reaction of Freon (CF₂Cl₂) induced by a TEA-CO₂ laser has been reported recently by several authors. The present work shows that large effects on the chlorine isotopes are also induced. Their laser-wavelength dependence has been measured, and some complementary information on the carbon isotopic effects has been collected. Excitation around 930 cm^-1 yields an enrichment in ³⁷Cl in the residual CF₂Cl₂, and excitation around 1085 cm^-1 has an opposite effect, while ¹³C enrichment is found around both 1090 and 922 cm^-1 and ¹²C enrichment is found around 1065 cm ^-1. These effects can be qualitatively explained with the known fundamental vibrations ν₁ (922 cm^-1, stretching mode) and ν₆ (992 cm^-1, rocking mode) of CF ₂Cl₂. The efficiency of the photodissociations of CF ₂Cl₂ induced by a CO₂ laser is evaluated, and an effective threshold energy density of 3 J/cm² is found at 1089 cm^-1.