13C-selective two-stage IRMPD of mixtures of CHClF2 and HI

The ¹³C-selective infrared multiple-photon decomposition (IRMPD) of mixtures of CHClF₂ and HI was examined in collimated and focused beam geometries using a CO₂TEA laser. The carbon-containing products were CH₂F₂ and CHF₂I. The former product showed remarkably high ¹³C atom concentrations beyond 95% under selected experimental conditions, while the latter contained 25% or less. The observed results can be explained satisfactorily in terms of the consecutive two-stage IRMPD process occurring in a single irradiation procedure, where the first-stage IRMPD of natural CHClF₂ produces ¹³C-enriched CHF₂I via the insertion of the initial decomposition fragment CF₂ into HI, and the second stage is the subsequent ¹³C-selective IRMPD of the CHF₂I to form a CHF₂ radical and an I atom. The CHF₂ radical reacts with HI to form CH₂F₂. Decomposition probabilities of ¹²CHClF₂ and ¹³CHClF₂ were measured as a function of laser fluence to optimize enrichment conditions. Furthermore, partial decomposition probabilities or relative production yields were measured as functions of laser line, pressure of HI, and pressure of CHClF₂. Both stages showed high ¹³C selectivities in the irradiation with the laser radiation around 1040 cm^–1 and at fluences below 4 J cm^–2. This mixture is one of the most promising chemical systems for the production of highly enriched ¹³C.