Organic gas/surface interaction: Fraction (γ value) of the kinetic energy used for ionization

When hyperthermal beams of organic compounds strike a heated Re surface, their positive ions are scattered from that surface. Within the energy range studied (several eV), the efficiency of ion production is a function of incident kinetic energy (Ek) and surface temperature (Ts). This indicates that the ionization probability (I) correlates well with both Ek and 1/Ts. The conversion efficiency of translational to ionization energy in collisions of superthermal molecules with a surface was studied from the resulting ionization behavior. The γ value, which is defined as a fraction of the kinetic energy used for ionization, is estimated from two unique Ek and Ts correlations. The gases used in this study were acetone, benzene, naphthalene, and α-pinene. The γ value was molecule dependent. For example, at one extreme is the α-pinene molecule whose γ value when derived from the I vs Ek relationship is 0.13 [the I(Ts) dependence gives γ=0.10 under the condition that Ek=4.5 eV]. Thus the γ values estimated from the two independent methods agree fairly well.