Photon energy dependence of satelite line intensity in the photoelectron spectrum of acetylene

The intensity of the satellite at 27.5 eV ionisation energy in the photoelectron spectrum of acetylene has been studied as a function of photon energy using synchrotron radiation. In the accessible range up to h{stroke}ω = 72 eV, the satellite is considerably weaker relative to the 2σ_g main line than at h{stroke}ω = 151 and 1254 eV. If the satellite is indeed of ²Σg symmetry, as both theory and c-2c experiments show, then the effect can be attributed to interference between 2σ_g- and 3σ_g-derived components of the spectral function.