
Butyl radicals (n-, s-, i-, and tert-butyl) are formed from the pyrolysis of nitrite or azo- precursors. The radicals are doped into a beam of liquid helium droplets and probed with infrared action spectroscopy from 2700−3125 cm-1, allowing for a low temperature measurement of the CH stretching region. The presence of anharmonic resonance polyads in the 2800 − 3000 cm-1 region complicates its interpretation. To facilitate spectral assignment, the anharmonic resonances are modeled with a semi-empirical local mode effective Hamiltonian that couples CH stretch fundamentals to HCH bend overtones and combinations