The 248 nm KrF laser excitation of alkyl iodide–fluorine mixtures. The production and spectroscopy of CF2(Ã)

Abstract

Emission from the Ã→X system of CF₂ has been observed following 248 nm laser excitation of gas-phase mixtures of various alkyl iodides (CH₃I, C₂H₅I, t-C₄H₉I, CF₃I, C₂F₅I, and n-C₃ F₇I) in F₂ and He. The CF₂(Ã) comes from laser excitation of CF₂(X) that is a product of dark reactions of the iodide and molecular fluorine and not from photolysis of some molecular species. An extensive progression in the ground–state bending vibration, 2⁶_n, with n extending up to 30 is observed. By fitting the data to an expression of the form G(v″)=W(v″+ 0.5)–X(v″+ 0.5)²+Y(v′+ 0.5)³ we obtain values (in cm^–1) for the anharmonicity constants of the bending vibration: W= 667.03, X= 0.3696, Y=–0.0118. Values have also been derived for the ground-state stretching vibration v^″₁= 1208 ± 5 cm^–1 and the cross-yanharmonicity term, x₁₂=–4.4 ± 0.3 cm^–1. We have corrected a previous misassignment of bands observed in the 248 nm laser excitation of CF₂that were attributed to the 2⁵_n progression but which belong to the 1⁰₁2⁶_n progression. Bands belonging to the 1⁰₂2⁶_n and 1⁰₃2⁶_nprogressions are identified for the first time.