Additivity and effective charge studies with light projectiles and target gases of CH4, CO2, He, Ne, Ar, Kr, Xe, Cl2, and Br2

The stopping powers of CH4, CO2, Cl2, and Br2 for light projectiles have been analyzed in terms of modified Bethe-Bloch stopping power theory in order to extract mean excitation energies (I) and Barkas-effect parameters (b), and effective charge parameters for low projectile velocities. Recommended values of (I, b) are (46 eV, 1.3) for CH4, (90 eV, 2.4) for CO2, (199 eV, 1.6) for Cl2, and (492 eV, 1.1) for Br2. The I-values for compounds lie about 10% (CH4) and 3% (CO2) above additivity-based predictions. The stopping powers of He, Ne, Ar, Kr, and Xe were similarly analyzed, but solely for extraction of effective charge parameters valid at low projectile velocities. ((orig.))