Analytic expressions are used to approximate the cross-section data for charge exchange between hydrogen isotopes and between a neutral hydrogen isotope and a helium isotope ion, and for ionization of hydrogen isotope neutrals by positive ions and by electrons. These expressions are then integrated over a Maxwellian distribution to obtain analytic formulas for the ⟨σv⟩ average as a function of the plasma temperature and the initial energy of the injected neutral.