ESR study of the photolysis of n-butyl iodide: Secondary photolysis and structure of the n-butyl radical

The photolysis of n-butyl iodide in argon at 4 °K has been studied as a function of photon energy and photolysis time, using electron spin resonance (ESR) spectroscopy to detect the free radical products. Photolysis at 2790 Å gives only the n-butyl radical, but photolysis at 2460 Å yields hydrogen atoms and some methyl radicals in addition to n-butyl. The n-butyl yield is approximately proportional to photolysis time for photolysis at 2460 Å, but the H atom and CH3 yields have a stronger than linear dependence on photolysis time suggesting that these species are produced by secondary photolysis of the n-butyl radical. The magnetic constants of n-butyl, determined from its ESR spectrum, are: g1=2.0029, g2=2.0030, g3=2.0025; A(α)1 = −29, A(α)2 = −18, A(α)3 = −21 Oe; and A(β1)0 = 46.5, A(β2)0 = 21.3 Oe. Axis 1 is parallel to the CαCβ bond. Axis 3 is perpendicular to the α-CH2 plane and lies approximately in the plane determined by the CαCβ bond and β-CH bond of the β-proton having the 46.5 Oe isotropic hyperfine splitting constant. The magnetic constant data also indicates that the α-CH2 group has considerable freedom for torsional oscillation about this equilibrium position.