Vacuum ultraviolet photoemission studies of nucleic acid bases

Abstract
The spectral quantum yields of adenine, thymine, cytosine, and uracil films were measured at photon energies of 7 to 23 eV. In addition, photoelectron-energy-distribution measurements were made at 21.2 eV. The photoelectron spectra exhibit features which can be associated with density-of-states structures below the vacuum level. The difference between the observed photoemission threshold of a solid film and the calculated energy of the highest occupied orbital for the isolated molecule is found to be 1.5–2.0 eV.