Isotopic effect in the (2+1) REMPI spectra of 13C-substituted methyl iodide for UV selective dissociation

To investigate a possible means of achieving isotopic enrichment of methyl iodide (CH3I), we studied the 6s Rydberg states of 13,12CH3I by (2+1) resonance-enhanced multiphoton ionization. For 3 ; 3 1 0 band (v3 hot band) excitation (at a full width at half maximum of 14 cm−1), we observed a well-resolved isotope shift of +16 cm−1. The band shape, which has a broad shoulder on the red side and an abrupt decrease on the blue side, indicates that this resonance is ideal for enriching the concentration of the desired lighter isotope (the isotopomer).